All of the main chambers in Bristol (Guildhall, St John's, QSC, Albion etc.) offer minis. I would have a look at their websites as they will all have independent timelines and application processes. With minis, it is always best to apply far in advance as there is often an element of luck in securing them and they are very competitive. Also, sometimes the placement offers and then the actual dates they give you can be several months in the future so you do not want to be late to the game!