Check with the regular shops - ones which are discussed like crazy here in clubsnap.
However, you may not like it, but I think unless you are using the lens as part of your job or earning money from it, then don't get the lense until you have enough money set aside. Buying things on instalment is a way to overspend. Buy only if you have extra in your budget. make do with what you have.
Not a good idea buying tru instalment especially lens or camera. You never know how long you going to use it and further more how long ur instalment plan. After sometimes definitely you going to purchase another better one then the one which you still haven't completed ur payment will starting to sleep in the fridge. Why not just save first ur $$ and buy it once u have enough. Then after that can open a WTS thread once u feel sick with it. Then keep on BBB and SSS.