Not sure your location/etc. but this is something you should be discussing with both your local Juniper Partner and local Juniper Account team.
If you tell me your company name and general location, I can find you someone to reach out to.
I believe IP-source guard is a future SW feature for EX3400, although some on-line documentation says it should be there along with all other Port Security features; that is feature parity between EX4300 and EX3400 should be there.