Is there a decent sub for the Fa madagscar vanilla?
No, not really. I don't know of a 1:1 sub for it. FA Madagascar (Vanilla Classic) is a very unique vanilla flavor.
IMO one of the following vanillas will work nicely. It will change the overall taste, but yes, will work.
SSA Classic Vanilla 1%
SSA Madagascar Vanilla 1% --- it is not anything like the FA Madagascar
SSA Borneo Vanilla 1%
VTA Vanilla Classic 1.5%
Or, subbing an ice cream. I've made caramel ice cream mixes with FW Salted Caramel and those were tasty.
SSA Ice Cream 1.5%
FW Salted Caramel at 1.5% will still be front and center with any of those substitutions. It's a pretty strong caramel flavor.