Some pears are much more acidic than others - it sounds like you had some of those. Malic acid is probably the culprit and that's held mostly in the skin - so if you use the same source next year, peeling them may help a bit. If it was wine rather than perry, then a couple of years of maturation would help - but I don't think that's advisable with perry.
So, the question is ... did you make still perry or sparkling perry? As it's your first time, I'll assume you made it still. If that's the case, you can mask the sour taste simply by adding some sugar when it comes to drinking time (DON'T add it to the perry until then!!!!!). It may take a bottle or two of experimentation to get the amount right (start off with a teaspoon per bottle), but it's amazing how many faults disappear when you're experimenting with homebrew. Oh - you could do the same with sparkling perry, but all the stirring to dissolve the sugar would turn it into still perry anyway.
A second thought - you say "now ... we've added campden tablets". I wonder how many you added? Could it be the sulphur dioxide you're tasting? If it is, worry not - that taste will dissipate over the next couple of weeks.
Mike
EDIT: If you give us your recipe, it might help in being more definite about the cause. Oh - and welcome to Ish
We think its around 6.4% now its bottled.
