p41, indirect Fire.
"A unit used as a spotter for an indirect fire attack may be used to spot for more than one IF attack in a turn, but cannot choose more than one target to spot in that same turn"
In standard rules, one spotter is any number of indirect fire attacks (including artillery indirect fire attacks) against that one target. The one spotter could spot for both long tom attacks.
If using Advanced Artillery optional rules, p152 adds "A unit may act as a spotter for only one artillery attack at a time." So if using the advanced artillery option, you'd need two spotters, one for each long tom attack.
