You could try to submit without them and if it's needed the IRS will send you a letter, but they might hit you with a penalty plus interest, but maybe not. If these are for trades you made usually those are detailed in the return and that might be enough if it matches with what the institutions sent to the IRS. File electronically next time it's so much easier. TurboTax desktop version Deluxe supports what you're doing, is less than $80 and you don't have to go to the shipping store and pay all that postage, envelopes etc. The online version is a little more but probably worth it. Plus both import directly from most of the institutions depending who you're using.
