Looks like they were bought by Genesis Supreme.
The seal on my 2015 Econ slide hasn't had any issues so I haven't need to try to replace it. I have spent some time looking at it and it seems like a simple face seal about 5 inches wide. I would guess any face seal designed to work on a slide will work. I think a key to keeping the slide sealed is to keep the water off the face seal along the top. The aluminum strip over the slide keeps the water off and I check that to make sure it is sealed to the trailer well.
2017 RAM 1500 4x4 5.7 HEMI
2015 PCW ECON 18RBS