Shelf life of pond bacteria

Standing in the local pond shop yesterday I tried to find a good source
of filter bacteria, but left with nothing feeling pretty annoyed.

The shop once sold bacteria in a sealed bad impregnated onto a foam pad.
It makes sense that the bacteria should colonise the pad in good
numbers. The pad was slightly damp and I think there was a shelf life of
a few months. What I have problems with are the 250ml bottles of filter
starter that have no manufacture or use by date.

I would be interested to know if anyone in the UK knows of a good source
for cultured pond bacteria, live on delivery. I'm not looking for the
pre-colonised filter media, perhaps a solution or pad that people know
to work well. The ponds coming to life now, so I want to be sure the
right bacteria are taking hold.

Any suggestions would be much appreciated.
Regards David