There are a couple of ways to make referral work for your business and to transform it into a system for ongoing leads.

You are on track by finding realtors who are looking to sell land to international clients. I would do a couple of things to make sure they want to support you.

You can start by investing a bit of marketing to actually film the process of how it is to work with you and the realtor so that your prospective clients can get a glimpse. By doing this, not only will they enjoy 10-25% referral fee.

You can also help them in the sales process, by perhaps offering a one time consultation or a mock design to get your buyers moving towards the yes line.

I would do this base on a one time fee, because your clients can come back to you with more changes but at the same time you are becoming a long term marketing partner.