When it comes to Polaris I strongly reccomend 2 companies...
1st Walker Evans Racing! WER is a direct supplier for Polaris and does LOTS of testing directly with factory Polaris. Hands down some of the best products and service you will ever get! Best part is WER is a sponsor of UTVUnderground.com and may give you a discount for mentioning you are a member!!!
2nd FOX Racing Shox. So many companies are running Fox including Polaris themselves. There is lots of tuneability (is that a word) and lots of Fox's suppliers have valving specs per the Polaris products depending on the set up and terrain you run. Look to Magnum Offroad for Fox shocks!!! They too may throw you a bione by mentioning UTVUnderground.com
Bets of luck and FWIW I have heard lots of good things about the AFCO product line, I just have no first hand experience with the shocks.