I know it's not perfect but SJScycles do those DMR rollers that convert bottom to top pull. £7.99 a pop and you have to take the bracket and throw it away for the sake of the pulley wheel, but it's cheaper than ebay!!
They are under gear spares normally, or if you can find them, original avid rolla-magic things had sealed bearing pulley wheels on them and they work a treat (using one on my slingshot road bike at the mo)