Does any one know a good source for buying rubber to make rubber stamps?

Does any one know a good source for buying rubber to make rubber stamps? All the ones I can find on ebay, etc, are too thin, they are only 2.3mm thick. To make a good stamp you need a minimum of 3mm but preferably 4-5mm.

I looked even at craft store in the US without luck. Non of the ones I went had rubber at all, most had linolium

I have some red rubber I picked up at the hardware store I can give it a shot! It’s found in the plumbing section

Let me know if it works @Alex_Krause . Sure hope it does.

Haven’t tried it, but maybe this will help?
http://www.nettally.com/palmk/RubberStampMaterials.html

Thanks for the link @SirGeekALot

This is what I have used to make rubber stamps with carving tools. Not sure how it would work with a laser.