Here you go - I hope this helps....
The rails are held in place by 4 bolts - accessable by removing (or partly removing) the head lining.... Here is a link to a set of photos for the job...
http://www.discoweb.org/roofrails/index.htm
Once you have fought your way through to the bolts... you will need to fill the holes in - as you posted... heres the tough part...
You need a Rubber Gromet - 1 3/8 Inch across (that's the size of the hole) this is about as close to 35mm as you can get.... And there lies your problem....
I ordered a set of the Steele gromets - as per the above post from the manufacturer... I am in Oma (in the Middle East) and they got them here in only 5 days!!! that's a mirracle with this postal system - and I ordered 10 - might as well have others to pass on locally if needs be....
Total price - 15 Rials or about 20 GBP....
there are other options - though I am waiting to get the job done myself and can't vouch for this... but in the UK a company called Anixter -
Industrial and Bespoke Component and Accessories Supplier - Anixter Components, UK will supply you with upto 6 similar items as a free sample... contact their Export division.... The product is a rubber cap.. Part No. 4302753 .....
http://buyfrom.anixtercomponents.co...;28S|1||4302753|AND||AND||)(D||1|4302753|0|S)
these are a 35mm dome plug - much more solid plastic - if you use these you might want to seal the hole with a thin layer of silicone sealant at the same time... probably not have to bother with the other types....
You might be able to source something locally but the closest I could get is a 32mm rubber grommet from an electricians... just doesn't do the job...
I hope this helps, let us know how it goes as I am waiting for a non-sunny day to get on with this job...
Cheers, Tony.