Just walk in to your bank and tell them you need a lot of money to speculate in the stock market. I'm sure it won't be a problem.
Brokers offer a leverage of 4 times your capital. You can use options, forex or futures to get more leverage. You can go to a prop firm to get more leverage, 20 times++. At any place, you can't lose more than the capital CASH you have or they will liquidate your positions. As for a loan, I never heard of any place that is willing to give away gambling money. If you have skills start a hedge fund or something. I guess if you are solvable, you coud get a loan at your local bank. I did it myself several years ago. Asked for 400k, little in net worth. No need to tell you their reaction. I made their day. If you can back a loan with assets I think a bank couldn't care less what you do with it?