Dudeman
Maybe it comes with part number 62511-17070-01 which is the large part in the pic. It isn't listed as its own separate part as far as I can see.
Thanks Dudeman, but I'd bet it's a separate item with its own number. Toyota are just crap at listing them for clips/retainers... but I will not give up so easily!

The annoying little buzz in the panel behind my right ear behind me must go!!!!
Mrskylighter
Does it need to be genuine Toyota and not aftermarket?
Could you get some used ones from one the MR2 wreckers in Oz?
I have found some aftermarket ones that look very close to what you have pictured.
http://www.vehicleclips.co.uk/ford-interior-trim-panel-plastic-trim-clips-door-cards-fascias-panels.html
Thanks Mrskylighter. Those Ford clips do look very similar. If I can't get track down the OEM MR2 ones, I might order some and see it they'd do the job.
I don't think used ones would be any better than the ones already on my panel. Clips like this always seem to be 'single use'. They never seem the same after they've been pulled out and put back in. I reckon that's one of the main reasons they start buzzing.