I've been doing a bit of homework on our belts, and it appears the stock belts on the 1UZ are a 6 rib type "K" section.
According to the industry standard metric designation they are called a 6PK belt (6P for 6 polyrib configuration). The generic reference for the early LS400 is a 6PK2240, and for the early SC400 is a 6PK2275, with the 2240 meaning millimeters of length, and likewise 2275mm for the SC belt. These are internal measurements.
For the American standard (set by Gates) they are still referred to as a K section belt, but Gates' P/N is a K060882 for the LS400 and K060895 for the SC400, with the K06 meaning a 6 rib polyrib configuration, and the 0882 meaning 88.2 inches, and the 0895 meaning 89.5 inches. Again, these are internal measurements.
With this decoding, it's pretty straightforward to find an 8 rib belt of nearly any length from 31 to 138 inches (780mm to 3500mm).
Justen, I have both the metric and imperial catalogs here, so if you know the approximate internal or external measurement of the belt you need, I can do a cut & paste of the Gates or Bando part numbers for a few that are in the range.
Note, If you have a broken belt, and measure its length, you'll have an external length which you'll have to convert to an internal length measurement. There are tables for this in the catalogs.