I want to ask for some help, inspiration, ideas with a trick that I am developing. Where exactly should I ask for this? I can't really find a suitable forum - unless I've missed it. Thanks.

There is a forum called “We Triple Dare You” but in your case you can not access it. Due to the nature of secrets discussed in such threads access is restricted to people who have 50 legitimate posts. This keeps it away from the public and search bots.

In lieu of that you may try certain areas which match up with what you are working on, be that cards, coins, prototype props or what have you.

If you clarify more specifics of what genre your idea is in, we may be able to better direct you to a forum for discussion.

I have an effect using the suspect cards in Cluedo that ends up with a kicker reveal in which the cards that are left in my hand at the end of the trick - that the spectator assumes and is convinced are suspect cards - are shown to actually have 'changed' and are now the weapons cards. I'd like to use these six weapons cards to run into another trick using the metal weapons from the game. I need a little inspiration and ideas of what would work. Whether these cards are marked (I have a set of marked weapons cards), or left ungimmicked depends on the effect that this leads to.

Looks like you are going to be somewhere between Gaffed and Funky or Deckless! depending on your method.

The answer depends on what you are actually doing. If the cards are marked or gimmicked, then the forum to use is gaffed and funky however if you are using strictly sleight of hand, the the workers forum would be correct.