The fact that the overwhelming majority of UMP supporters would support the CDU/CSU is an obvious one.
But some would vote for FDP (among them probably most of UMP-affiliated Radical Party and former Liberal Democracy supporters) and maybe also Die Republikaner.
The FN would frankly be all over the place, since there's no obvious German equivalent (besides die Republikaner, but they're too obscure).
Why not NDP?
MoDem voters would likely be on the SPD right, though I suppose some might be FDPers as well.
Some also would vote for CDU. MoDem have christian democrats among predecessors (though I don't know how much this fact affects current MoDem voters). And some may vote for Greens.
though I guess there are some socially liberal FDPers who would prefer the MoDem
Or Radical Party if it would run a separate list.
I think most of those 18% who can support Sarrazin wouldn't vote for FN.