I just did a manual workup of all 3-homer games since 1992, split out by team’s home stadium. Note that this doesn’t take into account stadium changes–for example the numbers for Washington include all 3-HR games by Expos or Nats hit at home, and all 3-HR games by visitors at the Expos’ or Nats’ home stadium.
Team H V Total
CHC 9 8 17
COL 8 9 17
TEX 9 7 16
CIN 9 6 15
BOS 6 5 11
TOR 6 5 11
MIL 7 3 10
PHI 2 8 10
CLE 5 3 8
ARI 4 3 7
BAL 3 3 6
DET 3 3 6
KCR 0 6 6
NYY 5 1 6
WSN 2 4 6
ATL 1 4 5
CHW 1 4 5
HOU 2 3 5
LAD 3 2 5
SEA 2 3 5
STL 3 2 5
OAK 3 1 4
SDP 1 3 4
LAA 2 2 4
PIT 1 2 3
SFG 1 2 3
TBR 2 1 3
FLA 1 1 2
MIN 0 2 2
NYM 0 0 0
So these are 3-HR games by home-team players, and by visiting players, and the total.
Check out the disparities for the Brewers, who have hit a lot more at home than their visitors have, and the Phillies, who have yielded a lot more at home than they’ve hit.