There are a couple shops in Paris that sell canned pumpkin (for like 5 euros a can...), and squash in general isn't that hard to come by.
Wrong season, though. I'm surprised you can find it.
For a pumpkin beer, there are two ways to go with the pumpkin: mash with it and treat it like an adjunct grain (i.e., use malt with a fair bit of diastatic power), or dump it into the wort kettle as a flavor ingredient. Mashing with it mostly gives fermentables, which is why pumpkins were historically used in brewing. Adding it to the kettle preserves a bit of the flavor and aroma, which is quite delicate. If you add it to the kettle though, be very careful to stir constantly so it doesn't scorch on the bottom of the kettle. I've never done it, or heard of it being done, but I guess you could put coarsely chopped pumpkin pulp into a grain bag to try to limit contact with the bottom of the kettle.
The best pumpkin beers I've had emphasize the malt and tend to be sweet amber ale recipes, although I've had an excellent pumpkin stout (Fisherman's Pumpkin Stout, Cape Anne Brewing, Gloucester MA). Hops obscure the pumpkin and clash with the spices.
What would you recommend in terms of finding the right blend? Spice tea?
Look at what goes into "pumpkin pie spice" blends to get ideas, then experiment until you find the blend you like. Making spiced teas and tasting them until you find a blend you like is one way, another way is to make sweet pumpkin dishes (pies, puddings) with different spice blends until you get the blend you like. For spice blends, it's really easy to overdo the clove and nutmeg, but you can add a lot of ginger without it being too dominant.
Once you've got your spice blend sorted, there are a bunch of ways of getting spice into your beer. Making an infusion (170 F water + spices) and adding the result to your fermentor or conditioning tank is one way to get spices in your beer. Another way is to put the spices in a bag and hang that in your conditioning tank for a while (a week to a month depending on spices involved, amounts used and degree of spice character). Yet another way is to make a cordial by putting the spices in good vodka and letting the mixture sit for a while (again, weeks to months), then adding cordial to taste at packaging time. Just be aware that spices can dry out your beer due to naturally occurring tannins and other phenolic compounds. Excessive levels can give unpleasant astringency. You really don't want to boil your spices, though, so don't put them into the wort kettle.