To follow up on this I still have a US frequency ISS lying around so I had a go at the US frequencies. Applying the same principle that Davis would pick nice round numbers and the channel gaps would be consistent I came up with the following set of frequencies.
Now they may need adjusting for however your oscillator is calibrated, but you should only have to add a constant offset to each channel. The channel gap is 501750 Hz
On my test RFM69 every channel has an REI of 0 +/-1, better than that in reality as 95+% have values 0 and -1 (1 REI = 61Hz)
static const __attribute__((progmem)) FRF_ITEM FRF_US[FREQ_TABLE_LENGTH_US] =
{
// Mark Crossley update 24/11/2021
{0xE3, 0xD9, 0xAE}, // 911400100
{0xE1, 0x97, 0xAA}, // 902368600
{0xE3, 0xF9, 0xCB}, // 911901850
{0xE6, 0xBC, 0x42}, // 922940350
{0xE4, 0xBA, 0x77}, // 914912350
{0xE2, 0x98, 0x8F}, // 906382600
{0xE7, 0x7C, 0xEE}, // 925950850
{0xE5, 0x9B, 0x40}, // 918424600
{0xE3, 0x39, 0x1F}, // 908891350
{0xE6, 0x1B, 0xB2}, // 920431600
{0xE4, 0x5A, 0x21}, // 913407100
{0xE1, 0xF8, 0x00}, // 903873850
{0xE5, 0x3A, 0xEA}, // 916919350
{0xE7, 0x1C, 0x98}, // 924445600
{0xE3, 0x99, 0x75}, // 910396600
{0xE2, 0x38, 0x39}, // 904877350
{0xE4, 0xFA, 0xB0}, // 915915850
{0xE6, 0x5B, 0xEC}, // 921435100
{0xE2, 0xD8, 0xC9}, // 907386100
{0xE7, 0xBD, 0x27}, // 926954350
{0xE4, 0x3A, 0x04}, // 912905350
{0xE1, 0xD7, 0xE3}, // 903372100
{0xE5, 0x5B, 0x06}, // 917421100
{0xE6, 0xDC, 0x5E}, // 923442100
{0xE3, 0x59, 0x3B}, // 909393100
{0xE7, 0x9D, 0x0B}, // 926452600
{0xE2, 0x78, 0x73}, // 905880850
{0xE4, 0x9A, 0x5A}, // 914410600
{0xE5, 0xDB, 0x79}, // 919428100
{0xE7, 0x3C, 0xB5}, // 924947350
{0xE1, 0xB7, 0xC7}, // 902870350
{0xE3, 0xB9, 0x91}, // 910898350
{0xE6, 0x7C, 0x08}, // 921936850
{0xE4, 0xDA, 0x94}, // 915414100
{0xE2, 0xB8, 0xAC}, // 906884350
{0xE5, 0x7B, 0x23}, // 917922850
{0xE7, 0xDD, 0x44}, // 927456100
{0xE6, 0x3B, 0xCF}, // 920933350
{0xE3, 0x19, 0x02}, // 908389600
{0xE4, 0x19, 0xE7}, // 912403600
{0xE5, 0xBB, 0x5C}, // 918926350
{0xE2, 0x18, 0x1D}, // 904375600
{0xE6, 0xFC, 0x7B}, // 923943850
{0xE5, 0x1A, 0xCD}, // 916417600
{0xE3, 0x79, 0x58}, // 909894850
{0xE5, 0xFB, 0x96}, // 919929850
{0xE2, 0x58, 0x56}, // 905379100
{0xE6, 0x9C, 0x25}, // 922438600
{0xE2, 0xF8, 0xE5}, // 907887850
{0xE4, 0x7A, 0x3E}, // 913908850
{0xE7, 0x5C, 0xD1} // 925449100
};