i know this is ikea, but sometimes they do have really good colourful/patterned fabrics.
you can get nice vintage/"retro" fabric from car boot sales also
ive baught fabric off ebay before too. but you do have to look through shit to find nice fabric on there. i got fuck loads of polka dot stuff for £10, more than youd get in a shitty fabric shop. oh it can be so barginous at times