This is exactly how you use a 1031 exchange to scale up. 

I'm wondering if there something like them but on a bigger scale.

I also don't know how day-to-day you are involved with your deals, but it sounds like what you are running into is a scaling problem (private lenders aside) - you can't do more deals because you don't have the bandwidth to do more. 

No way they can scale at that pace..

Moises, if you are planning to make it a business and you will be doing it frequently you will not be able to use traditional financing to scale up, which is the reason you have to go with asset based (hard money) lending, where we are not going to look at your debt to income ratio, like traditional banks do. 

I'm currently working on scaling up quickly through purchasing large SFR portfolios and/or apartments, and I'm in preliminary talks with a few sellers willing to carry back a seller 2nd note of 20-30% (i.e. the down payment).I'm looking for a lender that will move forward in financing the initial 70-80%, in 1st position, alongside a seller 2nd of the remaining 20-30%, totaling 100% CLTV.

Then you can usually eke out a small profit on the rental income if you self manage and pull your money back out so you can scale with that. 

What types of funding structures have you found most effective for scaling your real estate portfolio? 

Both private money loans and hard money loans are popular alternative financing options, but they’re different in key ways.Private money loans are like borrowing from friends or family, but on a bigger scale.

I've scaled through turnkey, BRRRRs and everything in between.