I make my own. 😀
http://www.petermclarenfineart.com/
Possibly the best way to buy art is direct from students at their degree shows, it can be a risky investment but you might get lucky.
I think the market is changing a little with the advent of artists producing their own websites, find an artist and contact them directly.
It’s also worth looking at auction houses sales of contemporary art, you can find some really well known artists work for not a whole lot of money. Don’t think that folks like Christies, Bonhams, Phillips or Lyon and Turnbull would be out of your reach, you’d be surprised.