There are 4 Kubota blower out there which will fit, as they are coming out with new models, so you may fine the old models, 2750 and 2755, and the new models, 5450 and 5455. They are a standard 50" and an heavy duty 55". I'm not sure what make the 55" an HD model, but thats what they claim. The HD model comes with hydraulic rotation standard, but its an option for the 50"
Technically speaking, you can also mount up snowblower from other tractors as well. Most, including Kubota's blower, are made by Rad Tech. I know for sure, the massey 2360 front blower mounts up perfectly, the only problem being the mid PTO speed on massey is different than Kubota, requiring a pulley change to get the right speed.
I haven't seen any after market front blowers that run off the mid PTO like the factory units do. You can get hydraulic drive, FEL mounted units, but they are super expensive.
I would stick with the kubota units, and just pick the size you want...50" or 55".