It took some time but with the 2019.24.1 firmware update, Tesla Model 3 finally can use the CHAdeMO adapter in North America.
The Model 3 has been available in the U.S. since mid-2017, but for the first two years, the Model 3 wasn't able to use CHAdeMO adapters, which have been available for Model S and Model X for years. The only way to DC fast charge was to use Superchargers.
In North America, Tesla uses its proprietary charging connector, so charging through other standards requires adapters (even the AC Level 2 SAE J1772).
After an update, the Tesla Model 3 will be able to use the same CHAdeMO adapters as Model S/Model X, sold in shop.tesla.com for $450 new. It means that the new capability is a pure software update.
There are currently more than 3,200 CHAdeMO chargers in North America, but those are mostly 50 kW chargers. That's not much juice compared to 150 kW V2 Superchargers, or 250 kW V3 Superchargers, but sometimes the chargers are better located/more convenient.
While CHAdeMO adapters are now secured, there is still no sign of a CCS Combo 1 adapter (the Tesla CCS Combo 2 adapter is only for Europe/other compatible markets).
EVgo charging network quickly noticed the availability of the CHAdeMO adapter for the Model 3 and released instruction on how to use CHAdeMO: