some free modules i found

https://github.com/SunboX/Add-Member-for-Boonex-Dolphin

Add Member module for Boonex Dolphin version 7.0.x. With the Add Member module you can add new members directly inside your administration area.

https://github.com/pH-7/Maintenance-BoonEx-Dolphin-Module

pH7 Maintenance Module for your BoonEx Dolphin website.

didn't checked them yet. no guarantee its working but its worth checking out.

Deano has a maintenance mod in the market.

The add member mod you mention is outdated and there is an updated free one; either in the market or as part of a forum post.

if its free why don't they put it on the market?