"There also people BC selling Gjallar for 800-1000 toks..."
^ is that true? That's ridiculous! LOL
I wrote a guide about this quest but I didn't put much info about the raid. I'm not sure if this is still how the raid works but I'll tell you what I did for my faceworm raids. After we beat the MVP, I would ask who killed the MVP and ask him if he got the Gjallar. If he claims there was no Gjallar then we would search for the another MVP. Yes, another one should spawn so you will have to search the map until you find it. You can kill the MVP as many times as you can but I think you can only get one Gjallar so you should leave once you have it. It's tricky I know, it's the most difficult raid in the server for me but we still manage to have some time to search for another MVP if we didn't get it the first time
As the party leader, you should not warp out of the map until you are sure someone has it. Also you should give more reward to the one who got the Gjallar so they would be encouraged to give it to you. I advise that you hire a full party so you have more time to search just in case and also only hire people that you trust. It's a really tough quest but if this is still how it works I don't think the drop rate should be increased to 100%