Things may have changed since the last time I spent time going through the dealers' listings, but Silix used to have a 6538 rep that had a case similar to what you might need for an A6538 & it was reasonably priced. So you might start there for the case.
Generally, I have found that, when attempting to recreate rarer models (i.e., the A6538), you should factor in the likelihood of some Dremeling or shaping modifications in your plans. In some cases, you may be able to piece together multiple rep watches to assemble something close. But if you are as neurotic as most here, it will take some finagling to get things to fit/look right.
Most jewelry stores will be happy to engrave a caseback for you. At least, I have never run into one that refused to take the work. However, I would avoid those that sell Rolex for the obvious reasons.
I assume this is your goal, albeit in modern form: