"Basically, looking for 1.8mm spring bars but with the full length of a 2.0mm and with thicker ends to take up all the room in the lug hole."
I know exactly what you are looking for.
One of the things I have is a big spring bar accumulation from many years 'collecting' and being a silent partner in a watch store.
Do I have any spring bars in 1.8mm tube size with long 1.2mm tips?
No. Never have seen any. Yet. But no doubt they are out there somewhere.
What I have seen is a few 20mm SB with 1.8mm center tubes and long .9mm +/- diameter tips in an assortment I got from S. LaRose 25 or 30 years ago. They are basically the same as a SB made for rlx 6694/1500 case with 19mm lug space and lug holes all the way through...they work in genspec Daytonas too. The catch is since they were made for 19mm lug space and having no 'flanges' on the ends, the 'shoulders' (usually 1.20/1.25mm diameter) on the ends next to the .9mm end tips can sometimes pass through 1.25/1.3mm lug holes and allow the SB to shift to one side.
Spring bars made for 16xx, 16xxx, and early 162xx DJ are similar to the 19mm SB except they have a 'plug tip' on one end and on the other end they have a 1.25mm shoulder ending in a .9mm tip. The shoulder might enter or pass through 1.25/1.3mm lug holes allowing the SB to stick out of the lug...but not usually.
'Plug tip' = the tip end that comes out of the tube like a 5512/13 etc SB.
'Official terms' = commonly used terms in the trade:
'Single shoulder' = shoulder on one end only, like the early DJ type SB.
'Double shoulder' = shoulders on both ends, like rlx 6694/1500.
'Single [censored]' = [censored] on one end only.
'Double [censored]' = flanges on both ends.
Spring bars for 6694/1500 etc have .9mm tips about 1.5mm long with 1.25mm shoulders on both ends.
Spring bars for DJ etc have .9mm diameter tips with a 1.2mm/1.25 diameter shoulder on one end. The other end has a 'plug end' (no shoulder) coming out of the center tube about 2.0mm long.
Measurements are approximate but close.