Not really, if WWII guns are hard for companies to sell (meaning not a lot will be made) then WWI guns will be even worse in that respect. Same for kit.
Most WW2 guns ARE WW1 guns. K98 and SMLE pretty much covers it. It would require a very small site to do trench warfare. Layout would be British MG nest, British Trench, German Trench, German MG nest such that the 2 MG nests are just out of range of each other. Then u give each side some objectives to complete in no mans land. use a sh*t load of Pyros and you would be able to make it quite scary. You could even plumb in some pipes with valves hidden in no mans land so you have to go ove...
Or each time you die, you take a bucket of water back to the trench with you, so everyone suffers if people die a lot.
It's not an issue of can it be done, more would it be viable to create the game zone and get the rifles and kit? It would have to be a permanent WW1 site so the rifles would have to be hire weapons, possibly the uniforms too.