go to your local caterpillar equipment dealer and talk to the parts department, they have a hardware and supply catalog that has bulk weatherstripping and window seals along with all kinds of other neat stuff. Also look online for hardware/supply company's that cater to the rv industry, Anderson hardware strikes a bell.
the memory isn't like it used to be try austinhardware.com they have a branch in Elkhart In for the rv people, also check a hotrod magazine for the ads for weatherseals.