It looks like the state's website has not been updated because GEICO is correct, the state of Nevada did raise their state minimum from 15/30/10 to 25/50/20. Because insurance companies are at the mercy of state regulation, it would be illegal for them not to comply.
If you're just looking for liability coverage then you should have multiple options. Unfortunately some carriers don't offer coverage for vehicles older than 1982, but there are some that will insure your vehicle.
If you want the dent repaired and the other driver doesn't have insurance then you can ask him to pay you out of pocket for the damage. If not, you'll need to file a claim with your insurance provider.
You should keep in mind that you will have to pay your deductible if you decide to file a claim. Since you hit a curb, it will be considered an at fault accident and your rate will likely be increased.
The buyer would have to insure the vehicle and list you as the "lien holder" on his insurance policy. This way, if the vehicle were to be totaled, you would receive compensation since you still have an ownership interest in the vehicle.
It would be a smart idea to have the policy go into affect on the day that you buy your car if that's possible. If you need to purchase a policy before the day you get the vehicle then you shouldn't have any issues starting it, but you would be wasting money on coverage for any days before you actually get the vehicle.