I bought a Masterpiece Arms in 6x47 Lapua and am very happy with it. You can chose your caliber, barrel contour and trigger. They use Stiller Actions. They manufacture the stock and barrels. I'm left handed and was limited in my choices.
Actually they will let you pick any number of actions. They prefer the Curtis at the moment but they built mine on a BigHorn TL3 earlier this year. +1 for MPA though, I love my MPA rifle. It's a hammer.
OP if you are serious about shooting PRS with it look really hard at the MPA chassis. It's designed for PRS matches. You should come to a match and check it out first if you can. You just missed one that we had on Saturday. There's another this month and another next month, and will prob be one in december also.
Also Mickey knows what he's talking about. Go with a custom action. You will be glad you did. It will last you many lifetimes. I know PRS shooters with 50k rounds on some custom actions.
But to answer your original question in this post, there seems to be a custom gun builder on every corner these days lol. But if you are going to put the money out make sure you go with someone reputable. PM me if you want a list, I've met a number of them at PRS matches. Especially the ones that put their money where their mouth is, and use their rifles in matches, and have others at the matches using them too.
There's always, of course, Terry Cross. Terry is involved in the PR game as well, but his specialty is of course building for LEO and Military.
https://www.kmwlrs.com/sentinel
If anyone is looking for MPA we keep 6.5 CM w/ cutris actions on the shelf. At Interstate Guns.