Cali is a big city and every Colombian city has a "moto street" where there are hundreds of small stores selling everything motorcycle-related. As long as you are not very picky about brands, I'm sure you'll manage to find something like a Pirelli MT90 or similar ... They will sure work on Saturdays, maybe even half day on Monday 24th...Closed on the 25th, but open again on the 26th. I can't point you in the right direction for the "moto-street" but if you ask a cab driver to take you there, I'm confident you'll manage. Just say "quiero comprar llantas para mi moto, por favor lleveme a la calle que tiene muchas tiendas de repuestos de moto" (or write this down on a piece of paper and show it to the cab driver). or Write this phrase in Google "llantas de moto en cali" and you'll have several addresses and phone numbers. Hope this helps. Buen viaje!