The Developer network (devnet) coins are Rubies. They have no real value and can be freely obtained both in Surf directly, and from devnet support.

The simplest way is by contacting support or the community at large. Please be informed that due to using unfair practices the distribution of Rubies is not available in Surf web version. 

Since devnet is used for testing purposes, it can, on rare occasions, undergo full restarts, that wipe all account and transaction history. In such an event you can request test Rubies again.