In case if you do not hold any Support Contract with Juniper for your Juniper product, you can still reach out to Juniper Customer Care Support Team and request them for one time courtesy support case to download JunOS S/w.
BTW, EX3200 H/w is considered end of life (EoL)
https://support.juniper.net/support/eol/hardware/ex_series/
https://kb.juniper.net/InfoCenter/index?page=content&id=TSB16343&actp=METADATA&act=login
Last supported junos version ex3200 being 15.1R7 (and its SR), stable version in ex3200 should be
Service Release 12.3R12-S12 or the 14.1X53-D48.