Sorry for the late reply. Looks like the majority of what you still need to level is Prime things. If you weren’t already aware those can be acquired from Void Relics. A large majority of the ones you still need to level are vaulted. Luckily two frames and their associated weapons are un-vaulted each month. You can check to see which are from the market in your ship under Prime Resurgence. Or by going to Maroo’s Bazarr on Mars and talking to Varzia.

The next large chunk of items are the Kuva and Tenet weapons which you get from the Lich system. This would probably be the most time consuming behind the Prime items you’re missing. For a full run down of how that system works i would recommend just checking the wiki page.

The rest are kind of scattered about so you can always refer to the wiki as to how to acquire them. The one exception to that would be the compainion weapons which you will get from building the normal and prime variants, leveling the Sister Hounds (which you will get from interacting with the Lich system), and leveling the Moas from Legs in Fortuna.

Hope that helps!

LR4 here, the screenshots might help with suggestions on how to obtain things in a timely manner. One thing to note though is that a lot of veterans like my self who have been playing for close to 10 years have been able to pace ourselves with the release of content to some degree. So while the total number of MR based items may seem high, it wasn’t always the case.