Hello UMD
I am a Dutch guy who wants to have a splosh session in the UK and provide all the substances, does anyone know where I can get large quantities of messy stuff without having a business of my own?

Also does anyone have any experience with traveling to have sessions?

Depending on who you choose to session with, you could arrange for them to buy the items (you could provide a shopping list and the money), or maybe go shopping with them before the session. I can't suggest anywhere you could get catering-sized items without having proof of business ownership. But if it's just quantity you want, going to Tesco would be about the same cost as going to a wholesalers - the benefit of a wholesaler is catering-sized packs and therefore fewer tins to open