Is there any philosophy that is similar or close to the viewpoint of that held by German philosopher Immanuel Kant as I need to put forward an argument from two Deontological ethical viewpoints.I have used the Kantian perspective, I now want to use one that is similar to it to strengthen the argument.
Marcia Baron takes a deontological line, similar to Kant's but also critical of it, in
THREE METHODS OF ETHICS: A DEBATE. By MARCIA W. BARON, PHILIP PETTIT, and MICHAEL SLOTE. Oxford: Blackwell, 1997. Pp. vi, 285.
Baron's own :
Marcia W. Baron, Kantian Ethics Almost without Apology
ISBN 10: 0801486041 / ISBN 13: 9780801486043
may be useful - she only says 'Almost Without Apology', which so there's critical distance as well as sympathy of viewpoint.
You might also care to take a look at :
Stephen Darwall, Deontology. Published by Wiley-Blackwell.
ISBN 10: 0631231129 / ISBN 13: 9780631231127
This is a collection expressing a variety of viewpoints; here you're very likely to find some useful material both sympathetic and critical.
There are well-known similarities between Rawls and Kant but these are not close and direct enough for your purposes, I think.