Just seen this. You probably have already done it but a good source of information will be the regimental HQ and \ or museum. A lot of the early central records, WW1 and before were destroyed in WW2.
The 19th Hussars are now part of the Light Dragoons. Their address is Fenham Barracks, Newcastle-upon-Tyne, NE2 4NP.
Hope this helps.