Opening or fixed windows? If opening, it's a generic D-profile that you can get per metre (same profile as door rubbers iirc), if you use Google you'll find places like Seals Direct that will probably have something suitable. Not sure about the fixed ones, but if you make a sketch with dimensions of the cross section and email it to said companies I'm sure they can match up something.
Thanks. For reference I ordered the following from Seals Direct: 4 x ETS2481 Small side seal. 11mm diameter bulb. To fit panel 1.5mm to 3mm £15.32 Arrived this morning and fits easily.