Mike,
According to Remington; they will only replace factory original parts. I.E., even if you send them an action w/o a barrel, they will only install a barrel in the original caliber. They DO NOT return any parts. I fought with them over a reworked trigger, that they replaced with a factory spec'd unit. I never did get my $75 trigger back. So, the answer is no, they won't sell you a bolt. The only way to get one, is to send them a rifle that has the boltface you want, sans bolt, and request a replacement. This they will do, and it's surprisingly inexpensive. I would just send them the barreled action, sans stock and trigger.
Your other options would be
http://www.gunpartscorp.com/, or Ebay. Remington bolts do show up there on occasion.
Good Luck....................Bug.