Impellor?
I did a google search on your M2 jet drive and found 1 easy hit. Any other searches led me to empty targets, even through Mercury. Though, with the Mercury website, it suggest that you go to your local dealer to replace this part. On line, the impellor will run you about $442 without membership. If you become a member, it's in the $300's and that's through a company called "Stem to Stern".
They had a lot of support for your engine and propulsion unit so it may be a good idea to become a member with them and get lower prices on all your engine needs.
On another note, during my search, they had a forum that I clicked into where people were posting about this new Mercury engine that had a jet drive. Everyone was amazed and talked about Mercury's excursion into the jet drives, with no luck in the 70's then discontinued. One of the posts described the power of the 240 EFI found in the Seadoo's........I smiled.
I hope this has been of some service to you.
Also, I see where you looked into SBT, did you call them? Because, even though it's not listed on their site, you may be able to take yous off and send to them to refurbish. They may not keep a refurbished in there catalogs.