Dallas,
the two sources I mentioned do have web sites,
Patrick\'s and
Stovebolt. Another possibility is
Jim Carter - I paid Jim & Kelly a visit about a month ago, and he has a number of rebuilt short blocks shrink-wrapped and ready to ship, at very reasonable prices (like a 261 for under $1500). I saw at least one GMC core there but did not ask the condition or price. Carter's is in the Kansas City area so shipping shouldn't be too bad.
But I agree with Tony that some diagnosis of your original motor is a good idea. GMCs are very tough engines, and unless it has some major trauma, might just need a some carb and ignition work, maybe a valve job.
