Here are some that I would recommend for games with Spelljammer type of setting: Sky Ships -- essential and on-point, this could cover most of your ship needs for a full campaign, https://marketplace.roll20.net/browse/set/1863/tra
... Alien Worlds -- surfaces, battle maps on different worlds to land on, this would be for up-close and yet plenty of elbow-room for long range, https://marketplace.roll20.net/browse/set/583/alie
... Planets and planetary system maps, and space backgrounds, take your pick or mix & match from these: https://marketplace.roll20.net/browse/set/1306/spa
... I've not included any monsters or token suggestions here, though. Many (any) from traditional fantasy D&D art packs, can work in SJ. The thread is open for more feedback from the community.