semi gloss

I use Testors enamel, and the only semi-matts they make are Black Chrome, which is a satin black, and a new satin clearcoat.

However, airbrush technique can create semi-gloss satin appearance.  If a gloss paint is laid down very dry/thin, it will not develop a high gloss.  If flat paint is put down with a very wet/thick coat it will have more of a lustre than when done as multiple thin coats.

Also, a flat finish can often be burnished with a very soft material such as Kleenex (but it does leave small bits behind which need to be cleaned off) or a very soft, clean rag.

Also, leather can be simulated by burnishing a flat paint with your finger- the oil from your skin makes a semi-matt lustre that is much like leather.

Before Testors came out with its semi-matt clearcoat, I used hardware store clear polyurethane thinned to airbrush consistancy.  Several brands of polyurethane offer a semi-matt/satin clear.

Tamiya,Gunze Mr. color, Alclad, Ammo, AK, all make gloss, semi gloss, and flat clears. Some, such as Alclad, are pre thinned. 

Humbrol makes a clear satin coat. Just add thinner. 

I do not know of any pre thinned semi gloss, flat or gloss top coats out there.

you can mix your own using Future and Tamiya flat base...