There are no MM's in Greys. That is why there is no quote. Any trading restriction was for the suspension, and is taken off by now. Schwab (and TDA) allows selling Greys on line. I know from personal experience. But, it is hit and miss. To buy Greys through Schwab (and any other broker) it takes a broker call, and subsequently higher broker fees.

To trade smart in the Greys (if "smart" is the right word), you have to call your broker and find out what their Bid-Ask is. Your broker's Bid/Ask may be completely different than all other broker's Bid/Ask, as well as whatever the current trading shows. It may be trading in the dark, but it is still constantly changing. If the Ask is acceptable you can tell your broker to place a buy order. If you really want to sell, and the Bid was acceptable, it is less expensive to do it online.

Be sure to ask about fees. Some brokers have surcharges that can add up. There is one that many brokers are now charging called an, "Illiquid Market Surcharge," for tickers under a buck.