Have you looked in the Library on this site? Here is the 1979 JBL catalog:
http://www.lansingheritage.org/html/.../1979-home.htm
It has the L212's with the UB212 bass module mentioned earlier, which was JBL's first consumer powered subwoofer, which I think premiered in 1978. That was all JBL offered in subwoofers until they came out with the L250 in 1982, with the B460. This was also the year that Audio Magazine published the article on using the JBL 2235 and 2245 woofers to make homebuilt subwoofers using 5th order alignments.
http://www.lansingheritage.org/html/.../1982-home.htm
I think the next year, 1983, or '84 they released the smaller B380 subwoofer using the 2235 driver:
http://www.lansingheritage.org/image...b460/page2.jpg
That is pretty much the extent of JBL's subwoofer offerings through the 1980's, so if you saw a catalog with a L250 in it and a different subwoofer, it was someone else's; JBL didn't do anything else with home subwoofers until Home THX came out in 1993 or so and they released the HT1S passive subwoofer, which was big, square, black vinyl, and crappy, so I can't see anyone pairing it with a L250.
So who's subwoofer did you see? Considering the timeline you mention (Late 70's/early 80's), subwoofers were not at all commonplace - Miller & Kriesel, who had nothing that could resemble a coffee table, or maybe a few years later a Sumo Samson, which was a JBL 2235 in a larger box with Sumo's Delilah crossover. I suspect the closest thing to what you describe would be the original Velodyne ULD-18, which I think came out in 1983, and was all the rage for the next 5yrs or so:
If it's not one of these, it's out of my memory, or possibly custom. I'm pretty confident, though, that it wasn't a JBL factory subwoofer. Good luck!