Most spark arresters these days are made specifically for existing models of bikes. The basic unit may be the same, but the plumbing varies by model.
FMF makes a universal spark arrester in either 1 1/8" or 1 1/4" and I believe these dimensions are I.D. There are few other out there anymore that are the old generic type we used to find at every bike shop. From the photo, your stinger looks like it may be smaller than 1 1/8". The smaller stingers also used to be quite prevalent. 7/8" used to be very common for MX bikes, some with no muffler at all if used strictly for racing. Back in the days when noise was thought of as a beautiful thing. On the other hand, many of the stock Hodaka pipes that had the built in arrester were 1 3/8" ID. The only thing I found that readily fit that dimension was the old VW Beetle exhaust tip. Slipped right in, glass packed, worked fine. I raced two years on that and still have the exhaust tip in the garage.
If yours is an odd size, you may have to build a stinger by cutting back the rear of the final cone until you get to the dimension you need, and then weld in a new stinger. Keep in mind that modifying stinger length and diameter affects performance, but if you are not building for that last half a horsepower, it should not make a difference in rideability. If I remember right, increasing stinger diameter generally lowers power peaks. Length of stinger can be matched to whatever diameter you are using to balance out the difference in power between two stinger diameters, to some extent.
DG makes generic silencers in standard diameters. Here are two side by side, the one with the small hole in the tip is 1 1/4" ID ( which is also 1 3/8 OD fitting old Hodaka Ace pipes ), the other is 1 1/8" OD, which is also 1" ID.
Here is shown the 1 1/8" OD silencer on a 7/8" ID stinger. The stinger OD is nominally one inch as is the ID of the silencer.
The point here is that there are still a few products out there but you will need to know the inside and outside diameter of your stinger, and verify which dimension a manufacturer is using when they say there's is 1 1/8" for example, so you get something compatible. Otherwise you can pick your product and make a stinger that matches, if you have welding equipment.
