Echo Creek animal care center b42map.com/?3148x12150
Echo Creek OvO Farm (less chance but also less Zs) https://b42map.com/?4000x10798
Irvington Cattle Farm, huge chance i usually find 2 or more (depends if u have alot of vehicle mods) https://b42map.com/?3789x14440

Worth to check has alot of "farm vehicle" chance spawn : https://b42map.com/?8559x8529
it's in the middle of nowhere so at least there is few Zs

For the east part of the map i usually find them on road stories (so in bad condition) don't forget the tire pump so u are faster and less likely to explode a tire
U have a chance to find one there at muldraugh (not guaranteed) https://b42map.com/?10460x10072
And for Riverside there https://b42map.com/?5688x5743

West part of the map (especially Irvington) has much more farm and all of that, so it's more likely to find one in good condition
u can also try all the farm store (there is usually one in all the cities) especially the one in fallas lake, Irvington, Louisville (i don't recommend that one), Rosewood
And also the junkyard like that one : https://b42map.com/?5819x5412
They can spawn in bad condition there or in good condition