Not completely sure how they get in JenBee, but once I had filled my pond with tap water, I left it for a month before stocking with plants (spring 08). By the time I came to add the plants there was already a small population of snails in residence. Apart from eggs (or v young snails) attached to pond plants, bird's feet and amphibians might introduce them I guess.
Have you put any planting pockets in your pond? If you have and have filled them with aquatic soil, you would probably get away with sticking in a few plants that should survive even now, although I accept availability may be a prob. This might have the added advantage of inceasing your chances of getting spawn in Feb next year. You are right though, patience is the watchword, but "everything comes to him/her (pc) who waits" - the almost daily arrival of new bugs and creatures in a new pond in spring is fantastic (Perhaps you should hibernate so the time passes quickly!!
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M