I have guide plates for $7.50 plus shipping (usually $1.50 for an "armored envelope").
You can use HPA, just be careful if you go full auto as I hear it can cycle too fast and make trouble. FWIW, I played for a full day on HPA and when I got home realized I had grabbed my co2 marker. I couldn't tell a difference, and it seems neither could the marker.
Just be aware that the seals for the CO2 marker are not readily replaceable, so try to keep liquid out.
__________________ rATS Project
: We have the technology, we can rebuild it. Shoot me a message if you need spare parts for your ATS marker. My feedback thread