I understand. The parts to “convert” a G36 to a SL8 are basically the furniture, not functional gun parts. If the host airsoft G36 is accurately replicated from the real G36, the specs should be compatible or close to it. The main SL8 pieces:

1. The front handguard furniture (basically a fiberglass/nylon shroud going over the barrel assembly)

2. The SL8 buttstock (incorporated into the receiver on a real SL8, but a removed “real” stock could maybe be kit-bashed together with the host airsoft G36 receiver? This would be the hardest part of the build, might require JBweld and sanding and re-staining to match)

3. The monolithic top rail with the sights. If the spacing is the same (or close to the same) on an airsoft G36 as a real G36, you should be able to affix the “real” rail to the airsoft gun. I believe it is a few screws in the rear and a nylon pin in the front where it attaches to the front handguard and barrel assembly.

The choices are: get real SL8 parts, 3D print or manufacture your own replicas, or maybe get a garbage-tier airsoft SL8 (I think Cyma or another Chinese manufacturer used to make a very low quality SL8 AEG? Can’t remember) and harvest the parts from that, to kitbash onto the quality airsoft G36. I’m guessing that option would require almost as much custom modification as using real SL8 gun parts. So really the limiting factors are OPs budget and manufacturing skill.