Here is an interesting thread about a underwater-Housing for a Pentax K-3:
Unterwassergehäuse für Pentax - erster Erfahrungsbericht ? Pentaxians
It seems the company BS Kinetics offered and made a whole lot of customizations. The user for example asked for an automated pressure control system and got that.
Here is the company:
BS Kinetics Unterwassergehäuse für digitale Foto- & Videokameras ? BS Kinetics Unterwassergehäuse
That is the most recent offer I can remember for a Pentax DSLR.
Probably not anywhere near cheap (most off-the shelf-housings for DSLR cost 4-digits anyhow, e.g. anywhere between $1700 and $3800).