MR43T need a replacement that is readily available at
autoparts stores, no junk please
I ve heard rapid fire #1 and nkg yr5 ngk is not that easy to find
ac is

If you just need something to get you going this weekend local auto parts stores will probably have auto version R43T plugs in stock. Same heat range and will work fine in your motor for short term use. They may begin to rust after a while. Nearly all marinas should have the MR43T's in stock.

Most places keep the rapid fire in stock I have 2 sets in the garage if you need them now try to find a set of plugs for your alu head blower motor on a sat afternoon.