Depending on what sort of equipment it is, you may be able to get documentation from the manufacturer.  For example, manuals for some equipment may even be available from the manufacturer's website and these will include the declaration of conformity.

Have you had training to do thorough examination of lifting equipment?

You could get in touch with your insurers to see how they can assist with this and other regulatory & statutory inspections they might help back you up with the initial TE so the bad news is comming from a 3rd party, and you get hero points for getting them back on track.

In the meantime, as Kate suggested you could get the relevant documentation from the distributor or manufacturer of the equipment so that it is in place when you have the TE’s done

Edited by user 27 July 2018 09:20:10(UTC)  | Reason: OP responded before posting

Any slings or lifting chains should have a tag that states the manufacturer, max capacity and the date of manufacture. They should also have a CE mark if appropriate. If you have these you can contact the manufacturer and ask them what the service life of the item is and then you can decide to either destroy them or test them. If they don't have these tags then destroy them.

If you decide to test them the test date should go on the certificate and the certificate should be kept for 2 years. Lifting accessories must be inspected at least every 6 months or sooner if the inspector deems neccesary due to the environment tthey are used in.