yeah, i figured the diodes had to be matched, which is why i didn't list the tons of "dual-series" pairs that came up. unfortunately, balanced modulators are easy to do in DSP code, so that reduces the amount of "real hardware" modulators in use by radio manufacturers. i figured such parts might be common in test equipment and radios that use balanced modulators for signal generation and up/downconversion, but it seems a lot of such functions have been moved into DSP, making most equipment a "black box" with very little of the work being done by real components.
hopefully, the 6-pin quads aren't too much hassle to use in place of the 4-pin ones. i know soldering jumpers to SMT devices can be a PITA.