In madrid Fotocasión definataly has it since i bought a roll there last week, for about 3.5€.
However, outside major cities the trouble is going to be FINDING small photography stores that will have it. If i were you and unless you're plannning to shoot more than its convenient to carry (50 rolls of 120 doesn't take all that much space up in a suitcase) i would definately bring my own stash. There sure as heck ain't gonna be any price advantages, specially with the wonderful 1.50 exchange rate...