Not sure on interchangeability amongst models (I know the crescents from NVs will fit a large frame NMBH/OV, but will slide on the bottom of the barrel leaving a scratch), but you can get crescent and bullseye ERs on both Brownells and MidwayUSA. Made by MK and Story. Be warned, I've had hit or miss luck with both versions being too tight in the ERH (easily fixed with a file and preferable IMO) or too loose (not much you can do aside from having sloppy fit. If I recall correctly, they run about $30.
1. The latest version of the Ruger ejector rods since 1984 are all the same, round and pointed on the end. They interchange with all Ruger's old and new models. Note: Large caliber old models had larger half round rods. But the new rods will replace them.
2. The New Vaquero crescent rods will work in any other Ruger except the 10" barrels with the long 5 " rods. Note: any Ruger rod replacement may take slight fitting to the slot of your housing.
3. Colt (only in blue and nickel) and aftermarket rods work in Rugers. MK Technologies makes SS Colt crescent and bullseye rod clones. The edge is not shaped exactly right but simple to fix (see below).
4. The MK and Story housings are expensive, but the MK has the correct curved slot for the Colt type rod heads to snug up tight to the muzzle. Note: I have never been happy with either housing to be shaped and fit exactly like the Ruger hsg.
5. The COLT ejector rod buttons make nice replacements for the Ruger ejector rod button.
Installing the Colt ER button in a Ruger is a no brainer. But here's my method to get the Colt button and Ruger's crescent button to nest up tight under the muzzle when at rest, instead of dangling like the Ruger crescent button.
Because the Ruger housing slot is straight and not curved like Colt's, I corrected the way it didn't tuck up tight against the barrel when at rest. It also works for the Ruger crescent button and old round button which also kind of dangle. It may not bother some owners but it's simple to do if it does.
I grind and polish a 'cam' curve in the end of the rod/button as shown below (Colts thread together, Rugers are riveted and may need slight re-peening). The curve must 'nest' or align with the curve of the housing attachment screw when the button is up tight against the barrel in a Ruger straight slot housing. The curved surface of the end of the rod contacts the screw under tension of the return spring and it will “nest” on the screw by "camming" or turning the rod and button tight up against the barrel. Works for the Colt 'bullseye' round ejector button as well.
You may also need to file just a small notch in the barrel side of the housing slot to allow the ER button to fold inward towards the barrel. So the button pops away from the barrel about 1/32" when in use and doesn't rub on the barrel.
On my Super Single Sixes I add a little additional curvature to the Colt button to match the smaller diameter barrels.
A Blue Colt rod and head assembly (they thread together, not riveted/peened like Ruger) is #160-205-003AD, $32.84 at Brownells.
But Colt does not make theirs in stainless. However Brownells also sells a Colt style by MK Technologies, and they do offer it in stainless, Brownells #737-400-101AK, $39.99.
I had to use the MKT for my stainless Montado.
As you can see above, it's flat on the edge but that was easy to fix by polishing to a nice Colt curvature, below:
Midway lists the mk and story rods as discontinued. Brownells has the blued mk in stock but no stainless ones. All my rugers are stainless so I guess my only option is to go with the stainless new vaquero rod.