Hello, Seasons Greetings!

I recently recieved a Nikon F3 setup and have a couple questions about it:

1. I can't seem to find how to change the ISO!?

2. I'm looking for a HP prism for the body, it has a DE-2(standard) prism already but I wear glasses so the HP would be ideal. Where could I find one of these besides ebay and craigslist?(currently ebay or craigslist does not have the HP prism listed)

Thank you!