.209 primer holder. Bit pricey I admit and not water proof but to reload outside of the safezone I think it's worth it easily dispense 1 at at time.
https://www.ebay.co.uk/itm/209-9mm-Roto-Loader-Airsoft-Blank-Firing-Grenade-Primer-Blank-Holder/223221505898?hash=item33f909df6a:m:mff478QwMrEqo4JB5CGzDcA
https://www.ebay.co.uk/itm/209-9mm-Roto-Loader-Airsoft-Blank-Firing-Grenade-Primer-Blank-Holder/223221505898?hash=item33f909df6a:m:mff478QwMrEqo4JB5CGzDcA