I suggest you contact the above mentioned individuals using a PM (Private Conversation) to open a dialog, exchange contact information, coordinate and get things started. Simply go to your user ID on the menu bar, click and click on "conversations" to get started. Then choose "start a conversation...."
There are at least four persons named above who have offered to help, or are situated to help. I am certain all would help if asked.
I suggest you NOT open a public dialog in this thread, so as to protect the privacy of the named persons who offered to help.
Of all of these folks, Ivar (el forum god) regularly mails things purchased in his shop (Casa Ivar) every day, and all around the world. I recall that he has some special postage rates as well. He is also regularly at the main post office on Rua Franco. So they know him on sight. You might start there.
Just a thought, while you are at it, you might purchase some items from Casa Ivar. It MIGHT be that the weight of your souvenirs might generously fall within the postage for the purchased items... Just thinking out loud...
As long as the Correos does not destroy the parcel, and you can authorize a third party to collect it for you, you should be "good to go."
I hope this helps.