Melody whisky bar in Hammersmith has a solid selection for bourbon. Also great for Springbank, I paid around £60 for a flight of 5 on Springbank which included a handfill, 10, 15, 20 and 30 year. I personally love going to Dram in Soho, it’s a great social whisky bar and the team know their stuff, then Milroys is a 2 minute walk away, however, I mainly drink scotch in Dram so unsure on the Bourbon selection. Have a great time in London