I get all my copper & acrylic stock from smiths metals near where I live.
www.http://www.smithsmetal.co.uk/
The biggest problem if you just want a small amount is they have a minimum order amount of about £30.
I'm going to hopefully start to sell small quantities of copper etc through my site in the future, but until my job calms down I have very little time for anything but sleep at the moment.
I'd also suggest asking in a new topic what is better to use than acrylic, as it tends to crack easily. Seem to remember someone saying lexan is much less prone to cracking. I only got acrylic as it was all they had in stock at the time.