Tellus 27 was discontinued many years ago - a close match would be a general purpose ISO32 hydraulic oil, no detergent additives (which will only keep debris in suspension and passing through your bearings). Shell are still helpful and a call to their support department in your country will probably get some suggestions that are a closer match!
Try getting Tellus 2 - ISO5 oil for high-speed plain-bearing headstocks, the only way is to mix the thinnest hydraulic fluid half-and-half with paraffin/kersosene...
There are some newer and possible better hyd.oils on the market now then back then....
Most of the sellers do have comparing info on oil so it's going to be an easy match I think
I have to change oil on some lathes in near future, it's all hydraulic oil and I will have only one type for all three of them
There are a number of smaller, non global (but still respectable) oil blenders who can supply suitable hydraulic oils. In the UK I bought oil from a company called Smith and Allan for my Bantam. They use Shell base oils, have a good customer service advice line and supply oil in 4 litre containers; what's not to like. They recommended their T37 oil as a substitute for Tellus 27. I guess there must be similar companies in Canada too.
I use Shell Tellus S2M on mine, without any drama ......that I am aware of. My lathe is a Chinese import so not sure what yours actually require, can you ring the lathe manufacturer and see what they suggest, if it is Shell oil what you require then google "Oil Shell distributor", ring one up closest to you and ask them to give you a contact name of one of their retailers. They should have a database of their retailers and what products they have ordered.