e is non-standard now, but used to be common. It survives as an option in many dialects, and often appears in folk songs.
e) I went to the post office for to buy some stamps. rk: This is nonstandard English.It's sometimes when people want to effect a really casual style of speaking but there's simply no need for both 'for' and 'to',
f) I went to the post office for buying some stamps. rk: We just don't use ' for + [verb+ing]' to state the purpose/reason.
f is not used to express purpose, but appears in uses like this:
On Sundays, some shops in the UK are open from 11.00 a.m.; but their doors open at 10.30 for browsing only.
There is an idea of purpose there I suppose, but the "for + [verb+ing]" is an explanation of purpose (rather than an expression of purpose).
[ I don't know what made me choose that colour.]