When there's a gold rush, sell pickaxes and shovels. Timothy B. Lee of Ars Technica writes:
The graphics card shortage is happening because high-end graphics cards are the best way to mine Ethereum and other non-bitcoin cryptocurrencies. With the price of these cryptocurrencies rising to unprecedented heights in recent weeks, a powerful graphics card can generate several dollars per day in cryptocurrency. And so a growing community of hobbyist miners has been snapping every graphics card it can get, creating shortages and high prices for everyone else.[...]
This pattern correlates closely with changes in the price of Ethereum. Graphics card prices started inching upward around June 2017—the same time Ethereum prices started to soar. The current boom coincides with the even more dramatic Ethereum boom of recent weeks.