Anyone have a 320d e90 downpipe the could sell me?

Hi Jay. 
have you tried quarry motors? 

Morning Jay

Technically there isnt a down pipe there should be a diesel particulate filter (DPF) if there is a single downpipe then it will be aftermarket. 

DPF's are normally really tough the bit that blows is the flexible pipe at the bottom BMW call it a Decoupling element and still sell them as will a number of aftermaket exhaust suppliers like Bosal

Try looking at www.realoem.com put the last 7 digits of your Vin into the search box then check the exhaust section. Once you have the part numbers just use the Internet to find the best deal or as Stu says Quarry have always been helpful 

Dave