I can’t seem to find any specs or teardowns for that light, so unless you can you’ll just have to measure carefully. Measure the widest place on the mcpcb. If it’s not one of the normal 16mm or 20mm as MtnDon said then you can reflow and use the old board, or sometimes you can carefully shape a board that is close in size and make it fit. If it’s one of the small boards those are a little harder to find but this one at least looks pretty basic/normal, so that’s good. For the emitter you measure the square base (it is likely about 3.5mm per side……5mm is the other most common size).
I suspect you have a 3.5mm (also called 3535 (3.5mm each side)) in the common Cree XP-L type. If so then you can pick from lots of emitters that use the same size/pattern. I might suggest the Samsung LH351D in that light, but the Nichia emitters and SST-20 are also great choices…even a good old Cree XP-L or XP-G. You can try to keep the same beam shape or change it a little, depending on what emitter you choose…and of course the color temperature.
Here are some trusted stores on Aliexpress.
Convoy (he always stocks good emitters in good tints/bins, so it’s a safe bet and he’s a wonderful seller): LED - Shop Cheap LED from China LED Suppliers at Convoy flashlight Store on Aliexpress.com
LHT Flashlight Store (great seller, tons of parts, they are the Aliexpress branch of Kaidomain…emitters are usually good, sometimes not the best bins): SMD LEDs - Shop Cheap SMD LEDs from China SMD LEDs Suppliers at LHT Flashlight Store on Aliexpress.com
Professional Outdoor Lightings Store (ok, similar to the two below): DIY- LED Emitter - Shop Cheap DIY- LED Emitter from China DIY- LED Emitter Suppliers at Professional Outdoor Lightings on Aliexpress.com
Wankedun Chain First Store (only used them once…have a little selection): Led Emitters - Shop Cheap Led Emitters from China Led Emitters Suppliers at Wankedun Chain First Store on Aliexpress.com
Hot Red Official Store (decent selection, lots of “mainstream” stuff, too): CREE LED - Shop Cheap CREE LED from China CREE LED Suppliers at HotRed Official Store on Aliexpress.com
For non-Aliexpress, here are a couple to try. Kaidomain is a big supplier. You’re ordering direct from them but as mentioned above they have their aliexpress store also. They’re reasonably dependable with good products and usually ok with customer service: http://kaidomain.com/Flashlight-DIY-and-Tools/LED-Emitters-or-LED-Star-on-PCB
Neven runs LED4POWER in Croatia and he is an advanced enthusiast. He doesn’t have as much of a selection but he’s a great option for some things (especially his drivers, but that’s a whole different level of light mods/repairs). Pretty fast shipping and he’s a professional in all aspects: https://led4power.com/
Also, here in the US we have a great supplier with Richard at Mountain Electronics. It probably would cost too much with shipping to you, but here’s his site anyway if you want to look around. He is like LED4POWER and Simon at Convoy in that he always stocks high quality items and is very much into parts and modding and creating drivers. LEDs