"Lack" can also be used with "for" in these two constructions:
1 - The concert was cancelled for lack of ticket sales.
2 - John and Jane have good incomes; their children don't lack for anything.
"Your argument is lacking [,] on scientific grounds."
This is a good sentence. But it doesn't use the collocation "lack on" (which probably doesn't exist). It simply follows "Your argument is lacking" with a prepositional phrase giving the reason - "on scientific grounds".
This was possibly the intention of the original, but with 'merit', I'd use "lacking in".