How can I find out if IBKR has stock available to short?

Übersicht: 

From IBKR’s home page at www.interactivebrokers.com select the Products menu and click on "Securities Financing" in the Services section. Scroll down to the section titled Availability List. From this page you can click on the link which corresponds to the country in which the stock you are trying to short trades. The stocks are listed in alphabetical order.  Find the stock in question and check the availability status. It is advisable that you also review the Overview of Short Stock Buy-Ins & Close-Outs article as this will contain important information regarding potential buy-ins and close-outs of short stock positions.

The other option is to access information on short stock availability through Client Portal. Open the navigation menu and click on Support. On the Support page you will see the Short Stock (SLB) Availability tool. Here you can type in different symbols and search for availability. 

Background: 

Be aware that short stock availability is a very fluid situation, constantly changing throughout each trading session. Because a stock is available now does not mean it will be available the next day, or even the hour or less. IBKR tries to maintain a short stock availability database, but it is not possible to have this tool update in real time.