Have a pro shop work with the Titleist rep. The online custom catalog would be where I would look for the part number, but I can’t find the link. Last I checked the TSR-3 weights were a unique animal. The TSR -1, -2, and -4 heads share the same weights. There are 3rd party weights for them, but not the -3. Titleist usually stops selling after the next release. Maybe the GT-3 will use the same weights?
In any event, it may take extra effort to locate a source. Maybe a local fitter still has the full set of weights on the shelf? Good luck!

An authorized Titleist retailer should be able to order them for you if they do not have them in stock.

Hi,
I bought a trs3 weights for my 3 wood, directly order from an official reseller of Titleist. My experience was easy with an excellent service.
So my advice is to order it from the retailer who sold your club to you. He should be easy to find.
The only thing is you have to know the exact weight you need for your club to arrive to the desire swing weight.
Good luck,

I did the same thing and found them on Golfworks. They are not official Titleist weights but they fit pretty well. I think Billy Bob's has them too. I like a pretty heavy swingweight and it is one of the things that is attractive about Titleist woods that I can dial it in pretty much exactly to what I like.