The bid, to be filmed for a TV show, involves laying 74 miles (119km) of track from Fort William to Inverness.
Love Productions, the programme makers, hope the "slightly bonkers" undertaking will be as popular as its Great British Bake Off.
Engineers and construction workers have also been sought for the project.
Construction is planned for two weeks over the summer and is to be filmed for Channel 4.
The working title for the show is The Biggest Little Railway in the World.
Producer of the project, Charlotte Armstrong, told BBC Radio Scotland's Out of Doors programme the new show would celebrate British enthusiasm for model railways.
She said: "It's massively ambitious. We want to bring together Britain's model railway enthusiasts and all the different skills they have, but also local volunteers, engineers and people with construction experience."
The programme would also celebrate a Victorian era idea to build a full-scale, working railway through the Great Glen.
The full interview with Ms Armstrong is to feature in Saturday's Out of Doors, which is broadcast on Radio Scotland from 06:30.
Model railway enthusiasts and volunteers are being sought for an ambitious plan to lay a model railway track along Scotland's Great Glen.