Basically, while in an IVA, your credit rating is shot and the banks are not obliged to open a business account for you. The best thing would be to try to speak to a business manager direct (phone or electronically) to see if he or she would intervene in the, usually computerised, application process.
A bounce back loan could also breach the terms of your IVA, unless you IP has agreed to you getting one, so you will need to chat with them also.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk