Can I use 'never once' like this?

While it is not wrong grammatically, why not try this expression which is a little less awkward:
"You told me there are a lot of them in this town, but (no comma) so far, why have I never once found such a thing?"

Also you might consider using not once, as an alternate phrase..but there's nothing wrong with never once, either.

Thank you very much.

you're welcome

You (had?) said there are lots of them in town; but so far, why--never once-- have I found such a thing? or

so why--never once--have I found such a thing? or

so why--not (even) once--have I found such a thing? or

so why--not once--have I found such (or "one")?

"You told me that there are a lot of them in town. So, why have I not found one?"

My preference:

"Though you've told me that there are a lot of them in town, I have yet to find one."

Good'n, Glen

I think 'but, so far,' is ok for stylist purposes.

I think 'but, so far,' is ok for stylist purposes.