I don't see why a #25 red filter would not work. I've checked the spectral sensitivity of Ilford MG paper (which should be fairly representative of most, if not all, VC papers); it seems to be insensitive to wavelengths above about 550-600 nm (see the Ilford pdf http://www.ilfordphoto.com/Webfiles/...0200232336.pdf )

A quick check of my B+W filter catalog shows that the 091 filter (#25) cuts pretty sharply and does not transmit anything below 600 nm (the cutoff seems to be at about 625 nm).

Get a good quality #25 red filter and cut it down to size and Bob's your uncle.

Best,

Doremus