Looking for a 300b integrated amplifier kit for my Avantgarde Trio (107db) horn speakers

I think Audio Note is the most well known.  If you want to go really budget, however, check out the kits from Asia.
I would post this question on a DIY board.  There are a few to choose from. Google DIY threads and see what you get.  I don't build but am jealous of those that do. My favorite non Audiogon-audio threads website is Audio Asylum they have a DIY Asylum as they refer to them as, it may be all tube kit however.

🙏 thank you, this is helpful

In your search for a 300B integrated amp kit I would strongly suggest you consider an Elekit TU-8600. You can find the kit for around $1200.00 without tubes at V.K.Msic or Tube Depot my suggestion would be VK as you get Victor Kung’s help and suggestions as part of the deal . The build is pretty straightforward although I made a stupid/ rookie mistake that Victor trouble shot for me . 
 My own TU8600 is fitted with Gold Lion outputs a Telefunken 12AX7 and HP5963’s in the 12AU7 position. It’s driving Zu Omen MKII’s or LS3/5a’s , and works well with either speaker in my large ( but lively) listening room. The Zu’s with their 97DB efficiency can play quite loudly in my 27’x19’ room while maintaining that exquisite 300B sound. The LS3/5a’s reach more modest levels but the amp really brings out the best in that lovely little monitor. I am familiar with Audio Note kits and believe you’ll find this kit comparable for substantially less money.

Found this site interesting and he has a 300b kit for $1,700. w/o tubes.
No interest in building one though.

https://www.transcendentsound.com

+1 re: AudioNote kit. Also look at Bottlehead Stereomour. Both fit the bill.