This came up at an event I was playing in tonight. It was a Legacy event, and I had prepared my deck before the event, but I had forgotten that my Tropical Islands were proxied, and failed to replace them, leaving my Tropical Islands at home when I went to the tournament. In round 1 game 1 I cracked a fetchand and went to search my deck for a Trop, when I realized my Trops were proxied. Obviously I didn't have access to Trops on the spot, and the store didn't have any (even if they did I wasn't going to buy them and they probably wouldn't lend them to me). In addition, the store's basic land box was currently in use at the time by another concurrent event and thus I couldn't swap out the cards immediately (or at least that was my understanding of the judge's explanation for his ruling; the exchange happened in Japanese so I'm not sure if I got the details right).

What's your call in this situation?

In a local event like this, I'm probably comfortable enough asking the nearby players if anyone has spare basics. Someone is bound to have a commander or standard deck or something. There has to be some somewhere

I agree, there have to be some basics flying around, even if other people are drafting at the same time. Did you get a game loss for it?

Game Loss, absolutely; replace illegal cards with Basic Lands (if YOU can't find proper replacements, which you already said). I would raid the other event for 2 Forest & 2 Island (guessing, there) - not doing that seems a bit odd, but that's a Customer Service issue, and subject to circumstance, opinions, and such - it's not a policy issue.

Alright. That's not what the judge did; I'm not going to say what the judge did because it was highly unconventional and he'd probably get in big shit if I said what actually happened (despite him not speaking any English and thus not coming on this forum ever). It might be worth noting that while the event is technically run at Competitive (they use the trigger rules and so on as if it was competitive), the event tends to have a more Regular feeling to it, and Regular style deviations are common, which is what happened here.

There is no competitive lite REL. It wasn't a wpn premiere event. At regular if the HJ deviates, it is not reccomended, but it happens. Just talk to the judge and explain how to fix it properly.