Hi,
i can do that for you in a single day.
I will deliver two solutions, a specific one, for the form you already want, and a generic one, for you to display any page inside your (fully responsive) layout.
### proposed solution (specific)
1. create the page(s) with your site layout around the external's form;
2. check if the external page requires external libraries and, if possible (it's usually possible), display only what you're interested on.
### proposed solution (generic)
1. the same of the former, but you can insert any link to iframe whatever you want;
Please contact me if you have any questions.
best regards,
Marcos Viterbo