I would also use "pudieras"/"pudieses" because of the agreement with the past tense --they were the best people ever, but the listener can't meet them now.
I would prefer a present verb for the agreement with "podrías": "
son las mejores personas que podrías encontrar" --there is now a possibility to meet those people.
The only explanation I find now is that many people are quitting the use of the past subjunctive because it sounds pretentious to them.
In any case, the speaker/writer probably has in mind a probability that one can meet people like the ones he/she described, and that is why he/she is using "podrías".
@Poli: With "fueron" I would have preferred "que hubieras podido encontrar".
