It is not decommissioned, but you need to have Juniper support account to use it.
Here are the links:
https://migration-tools.juniper.net/
https://i2j.juniper.net/s2j/index.jsp
First login to your support account than follow one of this links.
Regards
Leon Smirnov
Please Mark My Solution Accepted if it Helped, Kudos are Appreciated too