Mirages are routinely forward based and support infrastructure is maintained at several critical locations around the country for them since they have always been an important part of the combat inventory. During Kargil, the fleet was forward based in Punjab and Haryana to get them closer to the battlefield (as IAF lacked IFR equipment back then).Gwalior is their base. They would not be stationed anywhere else as they do not have the facilities to maintain them unless it was pre-positioned.
The accounts says they were scrambled, ie not in the middle of a CAP. Unless IAF published that Orbat it means nothing. It is really frustrating following this being used to French press conferences publishing details hours after an action.
In this particular instance, the Mirages involved in the skirmish were part of a 8 bird detachment forward based in Punjab to carry out CAP / QRA. They are still there and performing their role.