I'm not a LA but I use long arm rulers for free motion quilting on my sewing machine. Have you checked out Karen McTavish's book, Custom Curves? It's mostly about cross hatching and curved cross hatching.
If you are a LA, the MQResource.com site has a lot of LA info. I hear a lot of them use DeLoa's Boomerangs for curved cross hatching, which you should be able to find via google.
I have found my 6" ruler is too small for crosshatching easily, so I bought an 8" Fine Line ruler from Accents in Design, and I think I could have gone with a 12. These rulers have pegs on top to help you hold them and hook side velcro underneath so they don't slip, but are a bit spendy. For me, they were worth it.