Never seen one, but it sounds like it'd be really easy to make. You'd need to purchase a safari top, then visit a local fab shop to make up the bar necessary for the safari top to strap too. One non structural loop out the back, that's removable so you can put a standard soft top or hardtop back on, to hold a safari top tight.
Alternatively look for a 91+ Family bar. It'll bolt into your Jeep, and it has the rear uprights to support a safari top
'91 Frankenheep YJ. 4.0, 4" BDS, Richmond 8.8, Titan 12k, 35" KM2's, rust.
'88 YJ, 4.2/4.0 head, +4˝" & shackles, BFG 33's (sold)