Hello pal.
Without pictures it hard to tell what exactly you mean. I’ve done a quick search on eBay and a whole new airbox unit ( which you will probably need ) your looking at like £50+ :(.So the fact you actually still have the structure base and sides is good enough for now….
📝If I was you I’ll stick and are filter in there.make up a new lid to surround the top of the box. Basically re copy the design of airfilter box.
📝If you have a pair of your mum’s/misses tights Laying about steal them!!! Cut them to size you need, put a TINY drop of oil on them(so it’s evenly spread) them attach over the top of the airbox to act as a temporary filter. MAKE SURE THEY ARE FIRMLY ATTACHED.