Heloc vs cash out refi on investment property

[Aubrie Caton]

Hello beginner investor here! We bought a short term rental property in December in Montana the house only had the top floor done so we bought the house and just completed the bottom floor, creating 300k equity. Now that we have finished we want to tap into that equity to buy more properties. We got our interest rate  at 3.65% so I was just going to do a heloc but can not find a bank to do this on an investment property. PenFed just stopped in April, so we just missed it . Our new rate with a cash out refi would be 6.5%… I need advice on what to do? Our credit scores are over 760 does anyone know of any banks offering helocs on investment properties still? 
Also we did heloc on our primary to purchase this home, so that’s why we aren’t going that route.
Any advice would be so appreciated! Thanks in advance!