Well this probably wont help you to find one but when i bought my Massey Ferguson 10 the person i got it off of converted to an MSD ignition on it and it worked good.
I would love to see details on that conversion, I'm curious on what they used for a pickup and coil.
I've had to learn way more than I wanted to about these SSI modules/ignitions. I went through 2 modules in 1 month and have 3 tractors that use them.
MH81 has posted some good info, I recommend you read Ed's website and he explains what tests you can do to determine what is good and bad.
Looks like you probably have an early gen system since you are working on an HH motor, mine are all later yrs OH160's, but info should be similar.
*First, make sure it's not the ignition switch going bad. Unplug the wires between the regulator and stator as they house the kill wire too.
*Check to make sure plug wire is pushed solidly into module. The are push in and epoxied from factory and can work lose.
*Make sure you do not have an chaffed wires. I also dealt with the feed wire from stator was bare as it comes out from under
flywheel tin, it was grounding out on block.
* Stators usually do not go bad unless a wire comes lose, broke or they somehow get damaged. I burnt one up as I got water under
flywheel then ran it with a chaffed wire. Still looking for a replacement.
I think Ed lists the resistance readings on his website for the different circuits.
Off the top of my head,
4000-7000 ohms for spark plug wire
125-150 ohms for feed wire from stator
If you figure you want a direct "plug in" replacement, go with the Overnight solutions ignition. Dale has done a great job in keeping the system as a stock one. All others convert to a battery ignition.
If you decide to convert to Ed's or Miller's system which converts system to a battery-coil set up, I would recommend buying from Ed's link to his buddy Mike Brown who sells a complete kit.
I have a buddy who designed a simple system for my tractor using jsut a pickup and coil, MH81 linked to my conversion also.
No matter how you cut it, for do a conversion you are in it at about $150. I recommend staying away from Ebay used modules, I can't see wasting that much money for a 40yr old part that may fail tomorrow when you can buy new systems with updated electronics and replaceable parts.
There are coming to light a lot of new sysems for these old tractors as guys are coming up with ways to get around the non working systems. Just need a way to trigger a coil to fire the plug and you are set.