If you have not converted already , you can use 8 speed sti shifters on a 7 speed rear,they work beautifully ,you just have to limit the rear derailluer so that it doesnt go into the spokes ,your just going to use the firt seven positions of the shifter. You can find some good deals on new old stock 8 speed shimano shifters on ebay. I use rx100s on mine with a new 105 rear derailluer and seven
speed cassette. If you want brand new you can use Sora but I hear they are cheap.