hi i changed my option in to include custom vehicles but now when i use the /buy it only shows the custom one and not the full list of the normal rust vehicles

Are you using all the vehicles? The issue isn't that they are not showing, its because the limitations of rust chat and the list of vehicles being too long, so ones at top of list will not been seen 

Yes, I have all of them before I added the custom ones. It showed all of them in chat, now it only shows the 5 custom ones