There are old Defenders and new Defenders. The older ones were the Model 25 (1940s-early 50s), the newer ones were the Model 925 (1960s-early 70s) and most 925s have brownish plastic birdshead style grips (very distinctive) and adjustable sights. Some later examples came with wood grips. For both models the front and rear sights are adjustable, the front sight for elevation, the rear sight for windage. From the description you provided you may have an older Model 25. I think the 925 serial numbers had letter prefixes while the Model 25 did not. Most of the 25s came with sort of fat black rubber or plastic grips. I have seen those at gun shows. I don't know if grips for the 25 and 925 will interchange, but probably not.
The newer 925 Defenders were chambered in .38 S&W but briefly available in .22 also. They all came in both 2.5" and 4" barrel lengths, with most having 2.5".
I'd check the usual places - eBay, GunBroker, maybe the larger gun parts houses like Numrich Gun Parts, or some of the custom grip makers. I wouldn't think grips for either model would be that difficult to locate as they are not rare guns. Regarding making your own, if you were a good enough woodworker, or know someone who is, it might not be that difficult. But it would help if you had a pair to use as an example.
A picture of what you have would allow the model to be pinned down.
One other item - If you have a 925, it would be a good idea to buy a new all-metal hammer spring strut from Numrich Gun Parts. The original struts use a Nylon component in the strut which breaks easily. The part is fairly inexpensive and is easy to install.
I have a 4" 925 from 1964 and it is one of my favorite fun guns. The only downside is the .38 S&W caliber ammo which is difficult to find and expensive when you do. I reload for mine. It's a good gun, but it would not be my first choice for self defense. Nonetheless it would serve if needed, far better than throwing a rock.
I have read that during WWII, the Model 25s saw some service as weapons for defense plant guards, and possibly even for some US law enforcement agencies. If you were a civilian during WWII, handguns were difficut to come by, and you used whatever was available. Also during WWII, the British used a very similar H&R revolver for London police service, and it was called the "Bobby." See:
Harrington & Richardson Bobby
I can't tell you the edition, but one of the old issues of Gun Digest, I think from the 1980s, has a fairly comprehensive article about the H&R Defender revolvers.