Call your local furniture/leather store and ask them.
Or try your local shoe repair shop...
You can also try "ink & stain" removers which professional pen shops sell. The brand is "Amodex." Its a good stain remover... which pen collectors use and it even removes ink stains from skin/fabric and other surfaces. Amazon, also sells it if you look online.
There is also this, from Amazon:
http://www.amazon.com/Lift-Remover-Marker-Graffiti-Bottle...
Or this:
http://www.amazon.com/WINK-Ink-stain-remover-stick/dp/B00...
Or, try rubbing alcohol... it removes ink/paint/stains from surfaces although I don't know about leather or how it will affect leather.
But I know that furniture stores, sell/carry leather care kits which also have stain removers in them.
good luck, we have leather too.