Tamtam

I don't know any good preexisting soundfonts for Tamtam only. If you don't want to make your own, Sonatina's is really good, but that would involve downloading a 300mb file for just the tamtam.
I would suggest going to to this website:
http://www.philharmonia.co.uk/explore/make_music/percussion/tam-tam

and downloading the file classified as "Long Mezzo Piano Undampened". After that, get a soundfont editor like Polyphone (link: http://www.polyphone.fr/ ) and use it to make a tamtam soundfont. It is the best way to do this.
Also, this is arguably the easiest soundfont to make. No loop is needed, set the volume envelope decay in the instrument tab to 6. That is it.

I'm using a soundfont called Roland Orchestral Rhythm for Tam Tam sounds.

I suspect it is proprietary but you can download it here....

http://soundfonts.darkesword.com/fonts/roland_orchestral_rhythm.sfpack

You will need to install SFPack in order to install the soundfont.

If you can't locate SFPack - let me know here and I'll arrange to get a copy to you.