Where do you buy your CDs these days?


I'm curious what online sites folks use to find CDs? I use Amazon, and especially their Marketplace sellers for used discs. But prices have become high and supply has become stagnant. I used to use several European retailers (Amazon UK and Presto) before the pandemic, but shipping is extremely slow these days and I've had more than one never show up at all and presumed lost. Surely there are other online retailers?
drowe
Here's a no-brainer:   go to your local public library, check out 20 CDs at a time;  preview in your car while driving over the next week or two.  Rip the ones you like at home, return all---FREE!!
Hi,
I buy used, mint or near mint condition CD's, from Discogs site.
I will go to Steve Hoffmans site online, to research opinions  on a particular CD I may be interested in buying. There is almost always a consensus, within the many posts, of what particular "pressing" ,of a certain CD, is the best sounding, and which suck: AM+ Japanese mini lp style, MOFI, etc., to name just a few.
You can then enter your choice into Discogs search bar, and find hundreds of sellers of the CD you want. It will list various prices, locations, and condition.
I click on $USD. mint or near mint, and I get a list, at various prices, and geographical locations of the seller, to choose from.
Very reasonable prices, and sellers have feedback listed by their name.
Very happy with the results. I have bought several hundred CD's, over the years.
To add:
You can usually preview the tracks on Discogs. If not, there is always youtube to preview first.
Not sure where you are, but I live in Tampa. There's an outlet here called Sound Exchange that has thousands of new and used CD's. They never used to ship, but now with the pandemic, they were shipping. Not sure if they will continue, but you can check with them. You can Google them and get their contact info.
I still buy CD's and enjoy their sound and convenience.  All of my purchases are through Amazon these days.  It is the best place to find obscure albums.  Vinyl, CD's, streaming, it's all good played through quality equipment.
@jbmays   Don't know about your library, but my library discontinued CD's three years ago.  All you can get now is downloads, and I think they are MP3's. 
Epilog: Today most CDs are mastered way to LOUD. You can find the problem described if you search for LOUDNESSWAR on youtube.
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Because of the LOUDNESSWAR, I do not buy new CDs ever.
LPs can NOT be LOUDNESSWAR mastered, so new albums sound way better on LP.
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DISCOCGS is always my go-to-site for CDs or LPs in physical form.
It is superb sorted and I can search for CDs with proper mastering printed before 1990.
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The proper thing to do than, would be to rip them with EAC (Exact Audio Copy) on a PC which makes sure by comparing the signatures with its database that everything is ripped bitperfect.
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After that I convert the FLAC to iTunes lossless ADAC with XLD.
.. to feed my non-oversampling DAC (Metrum Amethyst) and tube amp.
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best regards form Austria (Europe, not the kangaroos)
I buy new classical CD's and SACD's from PrestoClassical in the UK.  However, their shipping prices have just increased a lot, so Amazon Prime may become my source.
+1 Discogs.  I also use dr-wars.com First for checking the quality of the recordings before I buy anything,  very helpful.  and I then I can use Amazon Prime if cost is competitive. I’ve found some “jewels “ from them. And eBay too...
Cheers
Amazon & Smithsonian. Used on eBay. Used Oldies in the past but service and quality can be sketchy so no more. Locally Goodwill and a few reseller's work if you can examine the product before buying.
Nice not to be tied to your ISP or streaming service for your music.
Then there is always NPR - if you still have a tuner.
Not sure that anyone has mentioned this, but Deep Discount is also a good alternative for both music and movies.  
Besides Amazon and eBay, I would try Berkshire Record Outlet, broinc.com
Heavily classical, mostly remaindered or discontinued titles at good prices. CDs and some SACDs, DVDs and Blu-Rays. They also have some jazz and world music. I usually find enough of interest to buy a batch 1 or 2 times a year.
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Usually eBay for CD's, if you know a prime member Amazon can be okay. Lp's from eBay, Pop Market and Discogs I've had a few problems with lp condition lately but usually everything is fine.Pop Market has some interesting finds in the closeout section if your willing to look and now free postage. Pre pandemic I enjoyed going to new and used stores to rummage the bins.
You can't beat Half Priced Books and occasionally Goodwill but since I've added Pandora and Spotify, I rarely buy CD's anymore and have tons I don't even listen to.