3Lph, the stem came with the bike.
In fact, the bike was mostly complete, missing only the seatpost, saddle, toe clips, straps, tires, and tape. Got the bike on the cheap, and paid pretty much the going rate for all else. None of it was ebayed.
These stems come up often enough on the bay, and sometimes go for less than $100. Kind of a lot, but nice Cinelli track stems that are 35+ years old don't grow on trees. Finding your proper length may be another issue. 25.4 clamp, so Nitto track bars will fit em. Cinelli track bars are gonna cost you.