GFCI's are available at all home improvement stores. Wiring them in is pretty basic. One thing is GFCI's are very large and don't always fit in standard outlet boxes, but they do make an extension plate for them.
Personally I thing a grounding probe is useless. You'll get arguments with that. But a grounding probe is not a safety device. Companies that sell them don't make the claim that they are safety devices. They claim that it removes stray voltage that can mess up your fish. There is no evidence that stray voltage affects fish or that grounding probes prevent that damage, but to each his own. If you believe it, then why not, they are not that expensive.
Mike