I’d check here
And I know Tap has some pastel. (If you’re in CA Tap is a great resource.)
https://www.tapplastics.com/product/plastics/cut_to_size_plastic/acrylic_sheets_color/341
Rowmark has a beautiful line called “Colorhues” with some pastels. A lot of them are translucent though and you have to find a distributor. Gorgeous stuff though.
(Looks like this GF gal carries the Colorhues actually! Might drop her a message and see what she has.