"Easy to find"? Mouser seems to have 88 kinds of 1Gohm resistors, in various packages.
https://www.mouser.fi/Passive-Components/Resistors/_/N-5g9n?P=1z0vkog&Ns=Pricing|0
I bought myself a few dozen of the TE / Neohm 1/4w ones a couple years back (haven't had the chance to use them though, i still have a few scavenged from other mic mods).
https://www.mouser.fi/ProductDetail/TE-Connectivity-Neohm/RGP0207CHK1G0?qs=sGAEpiMZZMtlubZbdhIBIFho3SHfDXSt5nRQ4pdsqnc%3D
Those 2W ones are kinda uselessly physically huge by comparison (imho); might be tricky to squeeze into some projects.