There are a lot of other makes of US locos and stock - probably the best way to get an overview of what is available is to look at at https://www.walthers.com/
Also use the store locator with searches for England and United Kingdom etc to find stockists - oddly it does not give link to their web sites but a google search on the store name should come up with it i.e. www.railsofsheffield.com, www.gaugemaster.com, https://sawyermodels.co.uk
Also use the store locator with searches for England and United Kingdom etc to find stockists - oddly it does not give link to their web sites but a google search on the store name should come up with it i.e. www.railsofsheffield.com, www.gaugemaster.com, https://sawyermodels.co.uk