HD must be discontinuing gallon cans at their stores and making it only ship-to-store in 2 gal cartons.  If you search online, that's the only way you'll find it.   I picked up some today for $29 on the clearance rack.   That's the cheapest it's been in a dozen years (been floating around $40 for most of that time).

 

Just be sure it's fresh.   It has a 3 year shelf life.   The first three digits of the lot number will be

S y m where

• S says made us US (Somerset, NJ)
• m is the last digit of the year (e.g., 7 for 2017)
• m is the month 1-9 (Jan-Sept), O(ct), N(ov), or  D(ec)
• the rest are the day of the month, lot number, etc.

https://www.popularwoodworking.com/woodworking-blogs/flexner-on-finishing-blog/user-unfriendly-zinsser-bulls-eye-shellac

The nearest one to me is about 40 miles, but I may have to check and see if I can get a gallon. I'd put it in a plastic bag or bucket....for some time there were complaints about the quart cans developing a leak while sitting on the shelf. I never heard that about the gallon cans, but it won't hurt to be safe just in case. I put all (2) of my quarts in zip locks after I had one go bad.

I had one leak and mess up the floor.   The new one's in a trash can and plan to move it to a drywall bucket

Haven't been able to find Sealcoat in HD or Lowes in sometime. I get it at my Woodworking store. The turnover there is quite fast so out of date cans are not seen. Once went to a TruValue hardware store and found a can 4 years old. Took it to the counter and informed them that it was no good and that they should get rid of it. It was still there the next time I went to the store.