Is there any merchants willing or anyone who may know where to find a specific tailcoat?

[Alwin Alcott]

if you want custom creations you better put your request at the "wanted" section of the forums

 

[Alwin Alcott]

if you want custom creations you better put your request at the "wanted" section of the forums

 

[Amethyst Jetaime]

You can't 'alter' or mod most mesh that you buy from other merchants.  The few that allow mods will only allow you to change the texture or color. 

The exception is if you are able to find something suitable that is being sold as a mesh model with the intention of a merchant texturing it and reselling it.  You would need to find one that includes download access to the .dae or an .obj file so that you can take it into Blender and make your mods.  Not many do and those models that do include them tend to be pricey.  However generally this will be still be a lot cheaper than custom made work. 

[Lindal Kidd]

There is a very inexpensive Victorian tail coat, of the older type clothing layer construction, on the Marketplace.  Perhaps it might do?

https://marketplace.secondlife.com/p/Victorian-Tailcoat-Charcoal-Gray/715470

You might also ask in the Independent States of Caledon group chat (or get someone to ask for you, the group requires an invitation to join.)  The citizens of Caledon are a very fashionable lot.