Before you go and spend a lot of time and money, you might want to test and see if you, indeed, have a problem with your red safelights and the Herschel effect.
Find a negative that needs a high contrast filter/setting to print. Make one with your normal safelighting; make a second with the safelights turned off (i.e., in total darkness) and then compare the two. If they match, you don't have a problem. If the Herschel effect is present, the first print should be less contrasty and maybe more exposed than the second.
FWIW, I find I need red safelights with some materials (e.g., Foma Variant 111, which fogs quickly under fairly bright OC safelight illumination). OC filtration should work with Ilford papers, but do the test as outlined by Kodak in their tech sheet on safelights. AFAIK, Ilford papers work well with red safelighting as well.
Also, I have switches on all my safelights so I can turn them off individually or from a master switch when I feel I need to limit safelight exposure (long exposure/processing times, etc.). Some materials let me use brighter safelights than others, so I'll switch one or two off when needed or change filters.
Ian Grant seems to know a lot about the Herschel effect and which materials are affected. Hopefully he'll chime in here soon.
Oh, and to answer your question: there seem to be a lot of 5x7-inch OC or amber filters on eBay and the like for sale. Maybe one of those will fit your Legacy unit? If not, used Premiere 5x7 safelights (complete with filters) seem cheap enough. Kodak bullet lights are easy to find as well.
Best,
Doremus
