Hi, marcy,
I know someone who needed to ship medical supplies ahead. What she did was make reservations at several points along the way in private accommodations. Then just email the owner and ask them about sending stuff ahead, all said yes in my friend's case. In one or two instances she had to change the reservation to a different date because it's hard to know exactly when you will arrive, but that was no problem. She sent the packages out after she arrived into Spain, because sending from overseas might trigger customs charges or some other headache. Good luck! Laurie