My preferred vendor for M&H is Mega Parts.
My understanding is that M&H has an exclusive contract with YO and the several other vendors that carry it get it through YO. I've bought through YO with the 30% coupon, and been frustrated with back orders with no updates of when your harness will be delivered until one day months later it shows up. At least with Roy and Jamie at Megaparts I know they'll keep you informed about any delays or problems with your order rather than leaving you hanging!