I'm surprised OP can't find a builder for a Keirin-type frame.
If you know of a framebuilder in the United States or Canada who is interested in building and painting a keirin frame for that specification of components and with that severe of a geometry, let me know... I haven't been able to find one and I am actively searching. I listen to framebuilding podcasts and subscribe to framebuilding YouTube channels... All I have heard is "I won't build a track frame..." Prove me wrong: Who is willing to build a steel track frame?! I am a customer waiting to buy your product!
And it isn't that I literally "can't find a framebuilder"... It is my experience that Rinsei-san at
Rinsei Lab is producing the most well-built and beautiful keirin frames in the new era... The only two bikes I have built up now are
a 2018 and
a 2019 Rinsei Lab, and I absolutely love these frames: They are both wonderful and Rinsei-san is active
in documenting his process.
Though it would be lovely to have a bike frame built with these considerations in a more local context... Buying secondhand keirin frames from Japan is a roll of the dice—understandably. I'd love to find someone who'd be interested in building something like this for me in a native tongue.
Though, again, if you know of someone in the United States or Canada who is keen on building a keirin frame: Let me know! I am a potential customer... And holy hell: I spend enough money on keirin frames every year not to be startled by the price of it