You can get reading glasses to +3.5 diopters at your favorite drug store or dollar store. If that is not strong enough, you can get clip-on readers from Daiso (US$1.50 from the store or about US5 from eBay). This will get you to +7 diopters, which should be strong enough.

I have seen +5.0 available at Daiso stores outside the US.

Of course, you can get prescription lasses from your optician. These can be exactly matched to your pupillary distance and any abnormalities you need to have corrected. My optician charges extra for lenses stronger than +3.0.