Where can I find the new course that replaced SSD1?

It's called the Distributed Leaders Course (DLC). According to email traffic, DLC will be located on ALMS. However, just as with the former SSDs, you cannot manually enroll in them, you are automatically enrolled when you meet the appropriate criteria. From what I've read, DLC1 is closed to E-1 through E-3, and only E-4s will be auto-enrolled.

"- SSD I to DLC I: Soldiers currently enrolled in SSD I will remain enrolled for a period of six months after DLC I is made available in ALMS. If Soldiers are not complete after six months, they will be disenrolled. At that point only SPC will be reenrolled into DLC I. No action is required other than Soldiers continue to complete the course. If SSD I has been completed, Soldiers will not be required to take DLC I, but are encouraged to take it because DLC is part of the learning continuum, which is progressive to the next level of resident PME.

- Once DLC I is cut over to ALMS, Soldiers in the grade of E1 through E3 will no longer be auto-enrolled. Only SPC will be enrolled into DLC I from the date available in ALMS for enrollment."

https://www.reddit.com/r/army/comments/9f0o5u/dlc_over_ssd/e5utgf2