I recently bought a big amount of minced meat and spiced it with onion, garlic, allspice and unfortunately a big amount of salt. I tried to decrease the saltiness by adding bread crumbs and eggs; is there any better way to remove that excess salt?
Unfortunately once salt has been added to something it can't be removed, only "diluted". As you have already added eggs and breadcrumbs to the minced (ground) beef the best solution would be to add some additional minced beef or pork and make meatballs. It is difficult to give quantities as it depends on how very salty the meat is but start by adding about one quarter of the weight of the beef with extra meat and you may well be able to add some extra breadcrumbs (though bread contains salt so breadcrumbs will not reduce the saltiness quite so effectively). Form a small amount of the new mixture into a patty and fry it in a small frying pan and taste to see if the mixture is still too salty. We would suggest making a tomato-type sauce to go with the meatballs, such as the one for the Turkey Meatballs in Kitchen (p44), but don't add any extra salt and if possible try to use canned tomatoes with no added salt.
Without the egg and breadcrumbs you could cook the meat to make a chili con carne or a bolognese-style sauce. Again use tomatoes and stock which have no added salt to try to balance out the saltiness of the meat and you may again need to add some extra unsalted meat if your existing meat is very salty.
All of these dishes freeze well so can be stored in the freezer for later use if you end up with a large quantity.