The sports shop at Kad Suan Kaew used to sell bands like this but no longer so just wondering if anyone knows anywhere else that has them?

http://www.optp.com/products/thera-band-loop__thera-band-spc-loop-spc-12-quot--spc-series.aspx

I used surgical rubber tubing when I wanted some resistance exercise. But getting three different thicknesses, I was able to have three different 'weights' to use. You can buy tubing cheaply in any of the chemical supply shops around town.

Thanks for the suggestion I'll take a look.