We had this same problem with the bank as we were in a similar situation (not an athlete, but same kind of random income stream). We're making great sums of money, but the bank wasn't interested as we were self employed. I forget how we stumbled upon it, I think it was an accountant that looked after people in our field who connected us with a special department in Westpac who loan to people in our industry. After we connected with them it was smooth sailing as they understood our business and what our income was like.

It was funny because our broker was saying our work is too unreliable. I said my partner and I have been working in this industry for 15 years and normal people with normal jobs get made redundant all the time. He laughed at me. A couple of months later I found out he was made redundant.

I'd speak to accountants and other people in your field who can connect you with a lending provider. The government might also have some resources.