I want to bet that certain stocks will decline in price, but they have no options and there are insufficient shares available for a short sale according to my broker. Do I have any other way to take advantage of a potential decline in these stocks’ prices?
If your stock does not offer options then you can check with other brokers to see if they have hard-to-borrow shares available. That's a long shot but still a possibility.
Another possibility is an OTC agreement with a counterparty but this is only available for big players since the intermediary is usually an investment bank or similar.