Any microlight shop will sort you out. There are large yellow plastic funnels used by most people which come with reasonable filters, but the Rolls-Royce of products is something called "Mr Funnel", which comes in two sizes and both has a very good filter, and a stunning flow rate that is about as fast as you can pour.
One source of "Mr funnel" is
here but most microlight shops will carry it or an equivalent.
Incidentally, most government surplus shops these days sell "bendy spouts" for jerry cans with a coarse filter in them. Those work very well in conjunction with a funnel to prevent spillage.
If for any reason you don't like those options, the Light-Aero catalogue carries a fine selection of funnels.
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