How can I raise my handlebars when there are no spacers above the stem?
One or more of the three options

Change the stem to one with an angle, with such a short stem height gain will be limited.
Replace the bars with a riser bar, these will give up to 40mm, maybe more of you shop around
A stem extender (proviso -  not on a carbon steerer).

Presuming no carbon parts (bars, stem or steerer), replacing these is well within the capabilities of of anyone who is moderately DIY capable with basic tools (Hex keys should be all you need).