If you have a Yamantaka empowerment you should register for vajrabhairava.org. I am not sure you will find the "Praise to the Inner Dharmaraja" there (which if my memory serves me is probably the prayer you are looking for), but you will find various practices associated with Kalarupa (aka Dharmaraja) on the site, as he is the main protector for Yamantaka practitioners.
You will need to send your teacher's name and when you received the initiation along with your registration info, but the website is free.
Praise to the Inner Dharmaraja may also be found in Bob Thurman's "Essential Tibetan Buddhism".
I also like this prayer very much. My teachers told me to recite it it is better to have a Yamantaka empowerment and also receive the lung (oral transmission) if one wants to make a regular practice of reciting it. Though, as we can see from the books mentioned above, it is widely available.
In order to ensure my mind never comes under the power of the self-cherishing attitude,
I must obtain control over my own mind.
Therefore, amongst all empowerments, the empowerment that gives me control over my mind is the best,
and I have received the most profound empowerment with this teaching.
brtsal ba'i bkhra drin