You've hit upon a gap in the market. There's not much of a selection out there beyond some mounted Redoubt Mughal cavalry and the above mentioned Foundry figures. I've been looking for similar figures in both 15mm and 28mm for a variety of armies and periods from the mid 18th - mid 19th centuries without much success - a crying shame.
One way round it conversion-wise would be to do some frankenstein surgery on a rider and standing figure. Cut off the rider's legs at mid torso and mount it on the standing figure and model the transition, adding details where you can. Thankfully mail is relatively easy to model in green stuff or milliput. It helps that the waist sash is a common feature and would hide the join rather well.
Also bear in mind that a rider might well dispense with more cumbersome knee and ankle defences when on foot for the sake of agility. A Sikh Infantryman's lower torso may suffice for many dismounted Mughals with baggy trousers and slippers.
You may need to think outside the box a little for source figures, scout around amongst the historical AND fantasy figures - Fantasy mini makers often resort to Asian cultures for inspiration - e.g. Games Workshop's High Elves, many of which have ankle or calf length mail. You might even consider the lower torso of any European knight from the late 12th century to the late 13th century for low level mail skirt and mail leggings and feet. Just remove the stirrups.
I saw several stands selling 2nd hand sculpts at a convention recently. They may well be a good source of 'material.'
Keep an eye out also for the 25mm Historicals plastics that are coming out these days... Late Roman and Medieval Persian, Russian and Central Asian figures may suit the bill too.