Spring Barrett M82A1 to HPA

[SoVuuN]

Hello! 

I'm new to airsoft and recently bought a spring M82A1 from snow wolf for large polygons.
After playing one game I realized that it is very difficult to cock the 190 spring. 
Now I’m thinking about converting my rifle from spring to HPA, but I don’t quite understand how to choose the right spare parts for this task, can someone help me with the selection of spare parts?

Thanks in advance!