I use 6 inch velcro backed sanding discs that I buy from car body repair shop suppliers , they have holes in them for dust extraction , so not sure if they will suit your purpose, they work out cheap enough if you buy a box of 50 or 100 at a time , obviously there are different quality ones available and I do not buy the cheapest or the dearest , I think the last lot ( 180 grit ) were Mirka ( £12 for 50 ),I also get abranet from the same place but this is in small sheet form ( 9 x 3 ) but no finer than 320 is available, good stuff though ! I use for hand sanding or it will stick to a small velcro sanding pad ( 2") in the drill . The supplier was called JCA coatings they are in St Austell and Exeter , not sure if nationwide but you will probably find something similar in a town near you though .