what are difference between meaning of these sentence?
前边走来一个外国人.
前边走一个外国人.
前边来一个外国人.

Question

Answer

前边 走来 一 个 外国人
and 
前边 来 一 个 外国人. mean same, 
in the first sentence the important matter is that he walkes (not runs or rides)
in the second the important matter is that he's approaching towards us

前边 走 一 个 外国人 - means he walks in front of us, probably crossing our way or alongside

and 
it would be 走着, 走了，来着 or 来了 anywhere but "Elementary Very Easy Chinese level 1 with Fun"  textbook

Answer

Ibet the first one is acceptable while the latter two are odd and unusual.
前边走来一个外国人—— There is a foreinger at front coming to here.