I haven't been able to find any empty nail polish bottles readily available here at decent prices (best I found was $5 each, eep!) and my credit card is maxed at the moment which means no ordering from Transdesign etc :s *blush*
So what I do is buy $2 shop polishes and mix directly into half empty bottles. Helps that I bought a bunch of used and new good quality polishes off Trademe for uni and frankening for $20 (got about 25-30 polishes plus some Clarins glosses, score!). A couple of my Frankens have just been attempts to modify shades that I have bought which looked good in the bottle but just don't look nice at all on my nails. For these I poured about a third of the polish out and then started adding things in
Hope this helps too!
Purrtykitty - Just finished making a nail polish that looks as though it is the lovechild of Cali Girl and a Unicorn/stars/rockets/rainbows/fluffy kitties/cupcake/neon glitter orgy
Will post pictures in a few days depending on how long my current mani lasts - just got a bunch of new stuff today in the post and from my sister and I'm loving it!