Sounds like you picked yourself up a nice tractor. I took a quick look at the owner's manual for the SB2040 snow blower attachment listed on Honda's Power Equipment web sight and it looks like there is a bracket that attaches to the back of the tractor to hang suit case type of weights on, and it said the weights (26 lb each) are purchased separately, but I couldn't find a reference to a part number for them.
NHS means Non-Highway Service meaning they're not intended for use on something like a trailer. tractordata.com lists the size of the rear tires on your tractor as 18X8.50-8, so I would think you could pick any tread design of that size, and they'll work just fine.
Just googling 18X8.50-8 tire chains produces quite a few options. For metal chains, I'd recommend 2 link as opposed to 4 link. That just refers to the number of links in the perimeter chains between the chains that go across the tread. Here's just the first two that came up for me when I searched for tire chains and rubber tire chains.
18x8.50-8 Tire Chains - m. e. MILLER tire
18 - 8.50 - 8 - $119.00 : RubberTireChains.com, Traction without damaging your surface
One thing I do when putting my chains on is let the air out of the tires first. It doesn't really seem like it would make much difference on tires on lawn tractors, but it did on mine. Then I put the chains on as tightly as possible and fill the tires back up with air. I just weave some regular bungee cords through the chains on the outside of the tires to pull them just a little tighter. If they're too loose they tend to flop around and the centrifugal force could cause them to reach out and grab a fender or something on the tractor.
Post some pictures of your new machine if you get a chance.