Have a 2 inch shaft going thru a bracket and I need a collar to weld on to secure shaft with roll pin or bolt no luck finding collar - what do you call them and where can you buy them

Did you find what you were looking for yet?

Are you looking for a shaft collar or a weld on pin boss? A shaft collar normally locks (with set screws or clamping action) to the shaft. A pin boss welds to the base frame with a pin holding the shaft in it using a cross pin, like where the pins go through a loader bucket. If you are making weld on pin bosses a machine shop may have drawn over mandrel tubing, or similar in stock the size you want, that can be cut to the length you need. You might have to ream it out a bit for your fit and drill your own cross pin holes, or have them make the pieces you want.
Here is one outfit that sells DOM stock by the foot.

https://mysteelyard.com/index.php?cPath=40&page=3&osCsid=8a265fb1f7c258ef5d52e16e4388a0b1

Thanks for your reply never heard it called a pin boss - I ended up using a piece of pipe / that DOM tubing is expensive I only needed 4 inches for two pieces

MSC has them.

https://www.mscdirect.com/product/details/35463827

I have bought collars with a set screw at McMaster Carr.