I also need one (for a Number 7) and was about to ask the same question, to which - after a bit of searching - I've discovered the answer.
The tote screw for older Stanley Record 4-1/2 , 5, 5-1/2, 6 and Model 7 planes is a 'turnip' size - 3/16" x 20-thread, which is quite a coarse thread. (3/16" Whitworth is 24-thread, 1/4" Whitworth is 20-thread).
They can't be found 'off the shelf'.
However, small well-regarded UK company which caters for model makers known as 'BA Bolts' is now manufacturing the screws is response to enquiries. They're made in brass and are available from their eBay shop. Not cheap at £9.95 each (post free in the UK), but then for small batch production, it reflects the time involved.
Here's the link to the eBay listing:
Stanley Record Plane Handle -Tote Screw Fit 4-1/2,5,5-1/2 6 + 7 Spare New Build | eBay
Description:
Stanley - Record Plane Handle - Tote Brass Screw.
Fits - 4-1/2 , 5 - 5-1/2, 6 and Model 7.
Unit of Sale = One Screw.
Length is 5/8" measured from bottom of head to tip.
Will also supply a shorter version in production soon.
These are available for USA residents:
Stanley Plane Tote / Toe Screw Handle Screw 20 TPI 1/2" Long NEW *Rare Find! | eBay
$14.50
More modern Stanley Plane Tote / Toe Screw Handle Screw is METRIC: M5-0.8 32 TPI, a much finer thread. A US seller offers these:
Stanley Plane Tote / Toe Screw Handle Screw METRIC M5-0.8 32 TPI New Style | eBay
David.