New owner here question about 335 35 R17 availability and re calibrating speedo

[CSX]

Well, I talked to Discount Tire today and it seems like rear Michelin PS2s in 335/35/R17 are on national backorder with no ETA. I have heard of tire availability being a challenge, but for some reason I thought that was just for Pirellis. For those of you that have probably been through this before, is there always a backorder for rear tires on these cars? Is there a certain time of year or some way to get notified of when there's availability?

I am also looking into a 3rd gen wheel swap, since Michelin Pilot Super Sports are readily available for these wheels, but without an OBD connection I know it's going to require a splice-in module. The two current options appear to be Unitrax and Yellow Box - but I only see the Unitrax module as being advertised for gear ratio changes, not speedo recalibration. Is there a popular opinion on which one is preferred?

Thank you all!