Finishing plaster (East Ham E6)

I'm looking for a small amount of finishing plaster, enough to fill a hole about 2mm deep and about 60cm across and 40cm wide. Seems a shame to buy a 25Kg bag when I probably need 1-2Kg maximum. I don't have transport, so needs to be in and around East Ham. Thanks. I'm told it needs to be "fresh" so nothing that's been open for more than a month or two please!