You could try sourcing a local carpenter. I've had great luck doing that. Taking a look at them, they could use something like what Kenrick Sound uses for their big JBL models: an X-shaped base that supports at all corners while crossing in the middle. You can get very imaginative with this and get an exact match with your speakers. Lots of ways to go.
All the best,
Nonoise
All the best,
Nonoise