I use the Blackburn Outpost Fat Rack. You can install it with P-clamps in the absence of dedicated frame mounts.
The Robert Axle Project extend axle is one way to go but kinda pricey.
RAP and OMM are the same company now -- right?Old Man racks work for some bikes without attachment points.
Salsa also has the rack lockMight add a Problem Solver Seatpost Clamp mount to go along with the Robert Axle.
I was able to get one recently for my E06 (wanted OMM but was always out of stock). It is a nice rack and will work with the RAP axle with some longer bolts. I got the kit from RAP that included the axle, seatstay braces, etc and did a hybrid.I like the Topeak fat rack, but I'm pretty sure they stopped making those at some point in the past.