BuyKarma is an app for PayPlans which allow you to sell Jomsocial karma points with subscriptions.

Payplans is a highly flexible Subscription system which allows you to attach apps to each subscription enabling you to deeply integrate subscriptions into your Joomla based website. PayPlans is simple to use and flexible to a degree never before achieved (in our opinion)

Simply install the app like a typical plugin, attach it to the subscription(s) of your choice and configure each instance to give the amount of karma points you would like to sell, when a customer purchases a subscription with this app attached they will receive the amount of karma points which have been configured for the plan.