Just thinking out loud hear... But that plug should be standard pipe threads, so why not figure out the size needed (maybe someone knows off the top of their head) and go to Fastenal, Grainger, HD, Lowes etc and get a pipe plug for a couple of bucks max, verses $10.00 - $20.00 for one. Just throwing that it there.

But then again I could be totally wrong.
__________________
The Cub Pack. 70, 100 (creeper), 104, 122 (2), 1250, 1810, 1863, 2182, LTX 1050, SLTX 1050, SLT 1550, SLT 1554, Snow Chuckers 450, 451, 826T, 1030E, 2 plow blades. always looking for "just one more"