How can I get a recommendation for WO school if I have no WO in my unit in my field?

If your chain of command does not support you, find a WO in your prospective field and explain the situation for an interview and LOR.

Check with your accessions NCO. That person will likely know where some 920A's are. I know in the past this is a shortage area for WO's. If the rest of your shit is together, I bet that having a senior Log Warrant who does not really know you, sign off on your packet, will not be a big deal.

Again, seek guidance from your packet handlers.

Road trip my friend. Knock on every unit door until you find one. Make friends, explain what it is that you want to do and you should be good to go. I had a CW4 ready to recommend me and we never worked together. We worked in the same building and we always spoke to each other in passing. He knew of me and I knew of him and that was it. The first time I mentioned WO packet, he committed himself to recommending me. Good luck and Take Care Of The Soldiers!