I'm looking for a matte uncoated paper available in various weights with an old/retro feel. Not too brownish, neither sparkling white.

It will need to fit digital laser printing. The usage varies from brochures and flyers to office material. My client is a non profit organisation so it can't be expensive.
A4 and A3-sizes.

Perhaps you could suggest a glossy stock to contrast the matte as well?

Also, I'm on the lookout for envelopes with high opacity. One should be able to discern a logo through it.