Some individual tiramisu ideas for you Ivona...
First, figure out what size dessert you want, and what cutter you'll use. Then take the same sized can (of any food product), wrap it well in plastic, and then use that to make freezer paper 'collars' to help you make individual standalone desserts. Once you've figured out the freezer paper collar, that first one is your template, and cutting/taping 40 is pretty easy. Freezer paper is available in the grocery store, with the plastic wrap & waxed paper, and is quite sturdy (put the shiny side in toward your dessert for easier release).
Sponge cake, untoasted, will become pretty soft if it's combined with liquid/cream and left to sit for 2 days. If there's anyway for you to assemble them the night before, or the day of, so much the better. Both the sponge cake & cream mixture can be made up to 2 days ahead, easily, but if you're planning to soak the sponge (the way ladyfingers are soaked in a classic tiramisu) that's hard to do successfully more than a couple of hours before serving. You can, however, flavor the cream mixture with espresso to get the same overall flavor effect (and/or top the finished desserts with a little ground espresso in the cocoa).
Cutting the sponge cake is easy, with a round cutter, they're about $1 and are worth the investment since it has a nice sharp edge. Any waste scraps can be used to make another dessert, for another time, trifle - or - the scraps toasted & ground to be used in a cake batter.
If you're assembling your dessert inside the paper collars (make sure they're well taped along the cut edge, especially near the bottom) it'll take a bit of practice getting the first few right... but after that... you should be able to do them assembly line very quickly. It's easiest using a pastry bag for the cream mixture but you can use a large tip to make the work go quickly. Chill the desserts, very well, then remove your paper collars. I'd recommend coating the tops with the cocoa when they're still inside the paper collars, you won't get complete coverage, but it will keep the sides of your desserts cleaner (if that's the look you desire).
Good luck...
R.