Not sure about "telescopic" but:
Westaway Easy-Climb mast climber made from heavy duty polyester webbing fitted with slides to suit your mainsail luff groove from Westaway Sails, Erme Bridge, Ivybridge, Devon PL21 9DU tel 01752 892560
Um! Without the main sail up the boat is going to rock about pretty violently at sea. Can you cope? and what are you going to do when you cant get the main down at all?
I too like the idea of the mast ladder but I'm paralysed by indecision.
A year or two ago PBO had an article on DIY mast steps made of stainless steel strip. I thought that was attractive - but there are snags with that too.
Whatever you do, I suggest that you avoid permanent mast steps. Although they are convenient, in that they are permanently in situ, I have found that they are used most often to free something that has caught itself in the steps!