look for the part # 36-23-6-779-490 or equvalent...

the sensors in the tire are the part of the RDC system, that used the actual radio senders ( i think 315 MHz, maybe i am wrong, i have to look at mine), along with antennas (part 36-11-8-378-753) and a special module that would plpug in next to GM in the glove compartment area... was rather more common on E53s in non- NA distribution, the E38, some E39s... then BMW experimented with the ABS TPMS as it was less parts, weight but the drawback was that the drop in pressure had to be in vicinity of 20% to be "reportable" and if if all 4 tires lost pressure at similar rate, it would not report while the RDC would report 5% absolute deviation in each tire (it also had a sensor in the spare tire that reported to the rear right antenna, so the spare had to be oriented just right)...

check ebay for the part number, i am sure youcan get the set from Baltic states...