Have you tried Maidenhead Aquatics, if you have one locally?
Look on Ebay - check the feedback (obviously) and try to match the water at the seller's location with yours. For example, I bought some red cherry shrimps last year and went with a Scottish seller rather than a London seller as I have softish water, most of Scotland has very soft water and London has hard water. But don't get mixed colours as they interbreed and with cherry shrimps at least you end up with a tank of brown shrimps.
The downside to Ebay - or any on-line shop - is the postage