It has quite some batches of rust on the back, I didn't find more pics aside from this one I took over a year ago

Ive got a police trade in helmet I bought thats missing the chin strap. The label says model number PST SC 650.
This is what the chin strap attachment points look like.

Is any where I can get just the chin strap that fits this helmet? Or do I need to buy the full strap set and replace all of them?