Well I bought an L30 and can confirm if you bought used, got it as a gift, or for any reason can't contact your dealer or don't know it, Topping won't respond to your emails anymore. They did the first time, but now crickets when I explained the situation. It's a total loss, even if you wanted to ship it to them for the $30 it would probably cost, they won't honor the recall themselves. I'm not going to sell it as the liability is too much if it zapped someones stuff. Maybe sell it for parts only with full disclosure, maybe a repair shop could use it. Sticking with Schiit or JDS from now on, I'm over it.
Ouch, I feel for your situation. Although I do see the point why Topping won't provide a warranty.
In many (EU and US if I'm not mistaken) countries the warranty is the responsibility of the dealer and not the manufacturer. The dealer should take care of how he handles the problem with the manufacturer. Normally this provides a benefit to the consumer as even if a manufacturer would go out of business the dealer is still required to honor the warranty period for the products sold (and provide a repair and/or equal alternative). The dealer is also oblige to follow local legislation/consumer protection rules (which, depending on the country, could be more consumer friendly vs the rules where the manufacturer is located).
In this case (with no documentation/dealer to fall back on) your in a rough spot.
Although to be honest, you would be out of luck with most other brands. If not bought directly from the manufacture you need to go to the dealer. I even had this with Apple (which normally has a quite customer friendly warranty/repair policy). It could be that JDS and Schiit have more lenient attitude towards replacing/fixing second hand products, maybe someone on the forum has some experiences to share?
To make matters worst for you I can imagine that Topping is also warry of direct warranty claims. There are quite some "old" L30 for sale which the original owner already received an replacement for. Not saying that's this is the case for you, but it definitely doesn't help.
The best bet is to try and find/trace the dealer and claim warranty with them.
edit: in the EU the dealer still needs to honor a warranty claim (within the legal warranty period) even if you bought the product used or got it as a gift. Not sure if this is the case in the US but I do expect it to be the same.