If you achieved this by paying all cash, then you are losing money. 

I've used the search feature on this forum but didn't have much luck.Are there any US investors, hard money lenders, or groups that invest in flips outside of the United States, specifically in Europe (Netherlands, Spain, etc.)?

Listen to podcasts, read books, and if you plan to invest in the Netherlands find some resources that speak to that market specifically.

A hands-off garage conversion ADU is over $100, even doing much of the work yourself, it will be much more expensive than your estimate.Single ADU additions in single family zoned areas are typically one of the worse re investments. 

My name is Naomi Pinger and I am a private money lender.

I am wondering if anyone invests in this area can provide me with some referrals?

Explore my personal favorites, Set For Life by Scott Trench or The Total Money Makeover by Dave Ramsey, for invaluable financial insights.3.

If I refi cash out I can probably only get about $50k out of the investment property, any ideas on another way to get the amount I need that I may not be thinking of?

While I am a lender, I personally use hard money on all of my own investment projects.

I've been interested in real estate investing on/off over the last two years.