I’m confused as to whether you only listen to vinyl. If so, I can’t help. If you listen on CD as well, read on.
During the 80s and 90s there was quite a renaissance of Jazz reissues on CD but that has subsequently fallen off. One need only look at the current Blue Note catalogue to recognize this. There are still small specialist labels that continue to seek out and release previously unknown/unreleased recordings by major players.
If you don’t mind buying used as well as new, there is plenty of excellent Jazz available on CD. Are you familiar with discogs? However, if you are seeking to collect the complete catalogues of particular artists, then you are bound to be disappointed. I don’t see why this should bar you from exploring the riches that are still to be enjoyed but this is of course for you to decide.
As far as Jazz CD guides, none are perfect. The All Music Guide offers the valuable feature of listing both in print and out of print releases. I found this extremely useful as were the stylistic overviews that helped me put artists and recordings into a more organized context. At the same time, it has many reviewers, which means you must learn which reviewers’ tastes are consistent with your own. There is an online version with sound samples that I still utilize.
The Penguin Guide has been very popular. Although they can be rather idiosyncratic in terms of what they include and leave out, they review many Jazz classics that most will want in their collections. For this reason, I found the Penguin very useful when starting out. Unfortunately, they only list titles that are available in the UK at the time each edition is printed.
RE: whether there is anyone to take the place of past "giants", musical development is cyclical as is the case in all the arts. There are periods of exceptional creativity crowded with particularly gifted talents and periods that are less dramatically so. But there are plenty of excellent players still walking the earth. Unfortunately, the number of venues where one can hear live Jazz has become very small, indeed.
I hope this helps.