LSM makes them here locally as well.
http://www.lsmeng.com/Billet_Blocks_for_Sale.html They were also an excellent general/close to home performance machine shop for me back 20-ish years ago,
they did a stellar job machining a 360 and 400/451 for me back then....
but their billet block business seems to have taken over everything and now I can't even get a balance
job done. Happily went down the road a little further to Best Machine and was glad I did.