There would have been no trades between the AL and NL during their "war" (1901-03). After that, I believe, in order for an interleague trade to happen, the players being swapped had to clear waivers in their own leagues first. That tended to cut down on the number of interleague player trades. Instead, it appears that most transactions were players-for-cash. You can look at
team-to-team transactions at BR. Those waiver rules were lifted some time in the 1950s.