Are there alternatives to okra as a thickening agent? I had a go at making a gumbo last week, and it went really well. The only problem was that the okra proved to be fairly difficult to source (after several supermarkets and groceries, we managed to find a tin of the stuff in a specialist food shop).

Given that the okra is used as a thickening agent, via the mucilage that sweats out when cooking, is there any other vegetable based alternative that would help keep the flavour of the gumbo, and thicken up the soup? 

I'm specifically trying to avoid cornstarch or cornflour, since that would likely affect the flavour considerably. I was thinking potato, which is also starch, but that would also probably affect the flavour a fair bit. I realise that any alternative would have some effect, but would like to minimise it.
Filé powder (ground dried sassafras leaves) would be style-appropriate.   

Fresh okra is only just now coming into season in the American south.   I'm in Tennessee and most supermarkets carry fresh okra for most of the year (though it often looks quite sickly), and frozen year-round.

If it's something you enjoy, you might look into growing your own, as it tastes excellent when it's fresh picked and handled appropriately.