They did not hit double digit returns.

I am doing the same thing   ,   My wife and i have 815 , 817  credit,  and  I was expecting lower than 5%  interest rate for my investment  property  Pre- App  letter.  

We have given them an offer letter and waiting to hear back on whether they accept.

This can be in your accounting or PM software like quickbooks if you have it or just a letter you print and sign yourself with the date and put in the tenant file.

I was back and forth with my lender for a year just looking at properties and having her give me pre-approval letters.

My service was worthwhile - I earned an honorable discharge, some medals and letters of commendation, and the ability to access VA health care, which has been most valuable the times in my life that I didn't have any health insurance - but it didn't do anything towards my RE investing career. 

We have submitted several offers without a pre approval letter from a bank or showing proof of funds.

I would start by looking up the addresses on the county real estate website to find out where the tax bills are mailed and start by mailing a letter there.

Also, provide them with your approved financing and/or a proof of funds letter from your bank.

@Jonathan Bak with 150 calls and a 1% response rate for cold marketing like phone calls or letters (not closing rate) you are about where you should expect to be in terms of interested people.