Most Bible translators are unwilling to sell their translations to open source projects. OpenLP in particular does not have any mechanisms for encryption or locking of Bibles, and even some open source projects that do have locking mechanisms have been denied from distributing Bible translations.
For example, on the Xiphos website:
A common request is for a NIV Sword Project module. Regrets, no inquiry to International Bible Society, holder of the copyright for NIV, has ever been fruitful. The only way to get NIV support in Sword Project UIs is via unofficial means using texts available around the Web.
The Xiphos project even offered the International Bible Society $10,000, and they still refused.
In summary, you won't be able to buy Bible translations for OpenLP, or other open source projects, due to the unwillingness of the translators to offer it.