pleasehelp“But I rather have”
No.
I would rather (or
I'd rather) is a fixed idiom meaning
I prefer, I would prefer, or
I'd prefer. There is no
I rather, I did rather, I used to rather, I have rathered, or any such form.
rather isn't even a verb. Your attempt to force this idiom into a sequence of tenses pattern and then call them conditionals won't work. They aren't conditionals.
The version you are most likely to hear is this:
But I'd rather have something my dad can't sell.
Nevertheless, you can also have this (your second example):
But I'd rather have something my dad couldn't sell. (couldn't = wouldn't be able to)
CJ