Plano Power has a list showing the range of years each of Honda's mowers were manufactured.
Plano Power Equipment Online Store - Common Parts for Honda Lawnmowers by Model Number
The HR21 goes back a long way, and was made in it's various versions from 1978 to 1983. Hate to say it, but parts for it, especially the bag, frame and side discharge are going to be kind of hard to come by. The HR214s were made from 1983 through 1989. More of them out there, but again, a lot of folks didn't hang onto the bag and frame when they got rid of the mower. Patience and continual searching will pay off, but to be honest, I wouldn't expect a quick turn around on them unless you found the right customer, like I did who really wanted an HR214, or me, who really wants an HR21. In the case of the HR214 I mentioned. I did a rebuild on the engine, a complete service on the transmission, new rubber on the tires, new blades. By the time I got done and subtracted the cost of parts, I cleared $50.00. Folks just aren't that willing to spend that kind of money on 30+ year old mowers, despite the fact that the quality of the mower exceeds most anything on the market today.
Here's boats.net's page. A great place to start to look for information on the parts you're looking for. On the boats pages, you can look up the part you need, find the actual Honda part number and search for it.
Here's another handy tip using the boats page. Once you find the part you're looking for, click on the part number. That will take you to a page specific to that part, and will show you every mower Honda made that that part will fit. Then you can broaden your search by looking for other mowers since most folks will list things according to the specific mower they have not knowing some things will work on other models.
All Years Honda Lawnmower Parts
Good luck with your Hondas.