The Rosco #27 tube filters are $14.95 each in the current (#47) Rosco catalog. My local dealer will give me a 10% discount, even though I'm ordering only two. Check their web site (http://www.rosco.com) for local dealers. He said they could be shipped direct to my home. You may also be able to order direct from Rosco, at least their customer service folks were very prompt in replying to an email.
The catalog number for 48" T12 filters made of #27 material is:
110 08401 4812 27
The sleeves come with end caps, though these might not be needed with the red fluorescent lamps.
The #27 material is called "Medium Red". It's actually much darker than your standard red filter for black-and-white photography, more like the B+W-brand 091. Given the spectral transmission curve (in the little swatch book the dealer gave me, and at the Rosco site), I'll try some standard 48" tubes with the filters first. There's nothing to lose but 30 minutes and a few sheets of paper for testing, and it could wind up being much less expensive than the minimum order of 6 F40T12/R tubes.