Steadfast is still in business as RP World Models, but I am not aware if they make any Turks. Giles Brown of Dorset Toy Soldiers can likely come up with Turkish troops since he has lots of different bodies and heads.
4th Hussar is right about Dorset Soldiers Cem.
If you go to the website - and then click on "European Wars" - you can see both Turkish Mounted Cavalry and Light Infantry Turkish troops on foot - in action poses, pictured.
http://www.dorsetsoldiers.com/
Cavalry shown are Turkish Lancers, Officer with drawn sword and a Trumpeter.
The Turkish Light Infantry are shown as a Standing Officer, Standing firing, Kneeling firing and another Trumpeter.
On the same page are a variety of other troops - which with appropriate head changes - and/or arm changes - could also convert some French, Prussians, Russians, Austrians, Saxon troops etc - to a variety of other poses - including artillery. All can be bought as either castings ( to paint and/or convert yourself) - or as painted specimens - if you prefer. With a few arm changes, many other poses suggest themselves. The Officer could have binoculars to eyes - drawn sword etc. Standing troops could be throwing grenades, for example - by using appropriate arm change.
So - easy enough to begin with the straightforward Turkish troops - and with a bit more thought - other conversions might follow. Have a look at WW1 pages too - as many other castings appear which might also convert to Turkish troops.
Just drop the owner, Giles Brown an e-mail - with an idea of what you would like - and he will always come back to you with more ideas - if you want.
Best of luck - Johnnybach