A flash fiction on itself is a beautiful example of your very own writing skills. Besides, I know two ways to publish them for a larger audience.
Competitions and tenders
Many tenders for short story collections or anthologies are in fact tenders for flash fictions, due to a low word limit. And for larger pieces the practice in writing 500 word stories will make it easy to expand to 500 or thousand words more. When participating in tenders with a character limit just count the characters in your flash fictions to get a feeling for the appropriate length.
I won’t list or link open tenders, that’s a search engines job. The required genres or themes will help to kickstart a new flash fiction story.
I hope to be more competent on this point in the near future. Make collections of your short stories and/or flash fiction stories and publish them. Search for an overarching theme and make a story collection about something like strawberries…
Where and how did you publish your flash fiction stories? And are there favorites from other writers?