The nuts I use comes from
www.drafmodel.pl and comes in sizes from 0,6mm up to 2,5mm.From 0,8mm you can have them with or without centerhole.
The sizes are 0,6-0,8-1,0-1,2-1,5-2,0 and 2,5mm
For bolts down to 0,8mm I went to my local watchmakerstore and he had a lot of stuff for the modeller

The bolts I got was 0,8mmx5mm and the price was nothing to talk about.
It was around 0,15 euro each.