I sent you a private message containing some of my private suppliers... I hope it helps...
All of the C-Series saws used the same air filters --- C5, C5G, C51, C51G, C52, C7, C7G, C71, C71G, C72, C9, C9G, C91 and C91G
Then there are the saws that Homelite made that used the C-Series shelling such as the XP's and 1050 and so on...
Greg